Original Research Patellofemoral Pain After Arthroscopy Muscle Atrophy Is Not Everything Jorge Amestoy,*† MD, Daniel Pérez-Prieto,‡ PhD, Raúl Torres-Claramunt,‡ PhD, Juan Francisco Sánchez-Soler,‡ MD, Joan Leal-Blanquet,‡ PhD, Jesús Ares-Vidal,§ PhD, Pedro Hinarejos,‡ PhD, and Joan Carles Monllau,‡ PhD Investigation performed at Hospital del Mar, Barcelona, Spain Background: It remains unclear as to why patellofemoral pain (PFP) appears in some patients after knee arthroscopy and what influence the quadriceps muscle has on its onset. Purpose: To compare muscle thickness, neuromuscular contractility, and quadriceps femoris muscle strength between patients who develop PFP after arthroscopic partial meniscectomy and a control group and to compare functional outcomes between these entities. Study Design: Cohort study; Level of evidence, 3. Methods: A prospective longitudinal cohort study was carried out on patients scheduled for arthroscopic partial meniscectomy. Patients were excluded if they had preoperative PFP, previous knee surgery, or additional surgical procedures (eg, meniscal repair or microfracture). The following were performed preoperatively: magnetic resonance imaging to quantify muscle thickness, surface electromyography to analyze electrical contractility, and an isokinetic study to assess the strength of the quadriceps femoris muscle. Patients also completed a Lysholm functional questionnaire. Six weeks after the index procedure, patients were ques- tioned about the presence of PFP, and the same tests were repeated. The PFP group included patients who developed anterior knee pain postoperatively, while the control group included those who did not develop pain. Results: Of 90 initial study patients, 20 were included in the PFP group (23.8%) and 64 in the control group (76.2%); 6 patients were lost to follow-up. Both study groups were comparable on all of the analyzed preoperative variables. Patients in the PFP group had worse results in terms of muscle thickness (9.67 vs 16.55 cm2), electrical contractility (1226.30 vs 1946.11 mV), and quadriceps strength (12.27 vs 20.02 kg; all P < .001). They also presented worse functional results on the Lysholm score (63.05 vs 74.45; P < .001). Conclusion: Patients who developed PFP after arthroscopic partial meniscectomy had more quadriceps femoris muscle atrophy as well as a greater decrease in electrical contractility and muscle strength at 6 weeks postsurgically as compared with a control group. The PFP group also had worse postoperative functional results. Keywords: patellofemoral pain; anterior knee pain; knee arthroscopy; meniscectomy; quadriceps muscle atrophy; physical therapy Patellofemoral pain (PFP) is among the most frequently patellofemoral tracking, leading to excessive compressive observed pathologies in the field of orthopaedics. Its preva- stress to the patellar facets and PFP.17,37 For this reason, lence ranges from 16% to 24% of the population and is more physical therapy focuses mainly on strengthening and neu- frequent in female patients, with a 2:1 ratio.34,41 Between rostimulation of the VM, particularly its oblique fibers (VM 80% and 90% of patients respond favorably to nonoperative obliquus [VMO]), as it has been shown that VMO has the treatment, with physical therapy as its main pillar.18 Clas- most effect on patellar alignment.17,26,45 However, the VM/ sically, the suggested etiopathogenesis of this pain was a VL imbalance is not present in all patients experiencing muscle imbalance between the vastus medialis (VM) and the PFP,10 and some other reasons must be causative. In recent vastus lateralis (VL) of the quadriceps femoris. It was years, other factors have been associated with PFP, such as assumed that hypotrophy or lack of neuromuscular activity the neuromuscular activity of the external rotators and of the VM caused a lateral patellar tilt and abnormal abductors of the hip,46 the rotational abnormalities of the femur or tibia,20,48 and even psychological factors (eg, anxi- The Orthopaedic Journal of Sports Medicine, 9(6), 23259671211013000 ety, depression, and kinesiophobia).13 DOI: 10.1177/23259671211013000 Meniscal injuries are common conditions in the knee ª The Author(s) 2021 joint, particularly in sports medicine. In many cases, This open-access article is published and distributed under the Creative Commons Attribution - NonCommercial - No Derivatives License (https://creativecommons.org/ licenses/by-nc-nd/4.0/), which permits the noncommercial use, distribution, and reproduction of the article in any medium, provided the original author and source are credited. You may not alter, transform, or build upon this article without the permission of the Author(s). For article reuse guidelines, please visit SAGE’s website at http://www.sagepub.com/journals-permissions. 1 2 Amestoy et al The Orthopaedic Journal of Sports Medicine arthroscopic resection or repair is the treatment of choice, Surgical Procedure depending on the type of tear and the patient pro- file.29,33,39,43 In those cases, arthroscopic surgery is an The patients underwent surgery by the same surgical team elegant procedure that often results in remarkable (P.H., J.L.-B., J.F.S.-S., R.T.-C., J.C.M.) in the knee unit of improvement in joint line pain. However, a non-negligi- our institution. All surgical procedures were carried out ble number of patients developed characteristic and under spinal anesthesia (15 mg; levobupivacaine 0.5%). usually temporary anterior knee pain after the surgical Given the short duration of the surgery (a mean of 20 min- procedure. utes), a tourniquet was used at a pressure of 100 mm Hg Postsurgical PFP may be related to the muscle loss that above systolic pressure with prior exsanguination of the occurs after sugery.16 This phenomenon has been seen in limb. There were no differences in tourniquet pressure patients undergoing different types of knee surgery, such >50 mm Hg among the patients. The APM was performed as anterior cruciate ligament (ACL) reconstruction15 or through routine anterolateral and anteromedial portals in total knee arthroplasty.47 However, as far as we know, all cases. No patient received a femoral or sciatic nerve there are no studies analyzing postoperative PFP after an block after the operation. No drains were left in place in any case. arthroscopic partial meniscectomy (APM). Therefore, the purpose of the present study was to com- pare the muscle thickness, neuromuscular contractility, Postoperative Management and strength of the quadriceps femoris of patients who develop PFP after APM and those who do not. A secondary The patients had surgery on a day-case basis. All patients received the same analgesic, anti-inflammatory, and anti- objective was to compare the functional results in these coagulant medication during the postoperative period. All 2 groups of patients. The hypothesis was that patients who patients received a standardized physical therapy protocol develop PFP after surgery have greater muscle thickness based on immediate postoperative weightbearing with loss, reduced contractility, and less muscle strength as well crutches as tolerated and without bracing until a normal as worse functional results than patients who do not gait pattern was established. Muscle function was restored develop this pain. using targeted strengthening exercises for the quadriceps. They started from isometric exercises and progressed to open chain exercises over the course of 6 weeks. Range of METHODS motion was not limited and progressed as tolerated. A prospective longitudinal cohort study was undertaken between June 2015 and December 2017 in 120 consecutive Outcome Assessment patients scheduled for APM. The study was approved by Patients were allocated to a group according to their the ethics committee of our institution. The inclusion cri- response to a question regarding the presence of PFP at the teria were an acute symptomatic meniscal tear requiring preoperative visit and at 6 weeks after surgery (“Have you surgery in patients aged 18 years. Patients were ever had pain in the anterior part of the knee in addition to excluded if they had PFP before surgery, previous surgery the current pain on the medial or lateral joint line?”). The on the involved knee (including meniscal repair), or an patients answered this question in writing with the rest of associated surgical procedure (eg, chondral repair, ACL the outcome questionnaires. reconstruction) during the index procedure. All patients To quantify the muscle thickness of the VM and VL underwent surgery with a maximum of 6 months of evo- muscles, magnetic resonance imaging (MRI) of the thigh lution since the meniscal tear. No differences were found was performed on all patients before surgery and 6 weeks in the time of evolution of the meniscal tear between the after surgery. Those MRI scans were performed on the groups. injured and contralateral knee. A high correlation coeffi- Of the initial 120 patients, 30 were excluded per the cient exists between the quadriceps cross-sectional area aforementioned criteria: 19 had PFP before surgery and and the total muscle volume.27 The knees were imaged 11 had an associated surgical procedure. For the latter, on the sagittal plane on the same 1.5-T whole-body MRI 7 patients had meniscal repairs with suturing; 3 had asso- unit (GE Signa EXCITE) using a commercial receive-only ciated microfractures attributed to the incidental presence extremity coil. A topogram was taken, and axial planes were of a chondral injury; and 1 had a partial meniscal injury programmed in a T1 fast spin echo 2-dimensional sequence that was left untreated (Figure 1). (flip angle, 55 ; repetition time, 580 milliseconds; minimum *Address correspondence to Jorge Amestoy, MD, Passeig Marı́tim de la Barceloneta, 25-29, Barcelona 08003, Spain (email: jamestoyramos@gmail.com). † Parc de Salut Mar, Barcelona, Spain. ‡ Department for Orthopedics and Traumatology, Hospital del Mar, Universitat Autònoma de Barcelona, Barcelona, Spain. § Department for Radiology, Hospital del Mar, Institut Hospital del Mar d’Investigacions Mèdiques, Barcelona, Spain. Final revision submitted December 10, 2020; accepted January 12, 2021. The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto. Ethical approval for this study was obtained from Clı́nica del Parc de Salut Mar (CEIC No. 2014/5534). The Orthopaedic Journal of Sports Medicine Patellofemoral Pain After Arthroscopy 3 Arthroscopic partial meniscectomy (n = 120) Excluded (n = 30) Causes of exclusions: - PFP before surgery (n = 19) - Left untreated (n = 1) - Associated surgical Patients analyzed procedures: (N = 90) - Meniscal repair (n = 7) - Microfracture (n = 3) PFP group Control group (n = 22) (n = 68) Lost to follow-up Lost to follow-up (n = 2) (n = 4) PFP group Control group (n = 20) (n = 64) Figure 1. Flowchart of the study and enrollment of the patients. PFP, patellofemoral pain. (MegaWin), extracting muscle activity and the maximum voluntary contraction values of the VL and the VM during the preoperative period and at 6 weeks postsurgically. The Ag/AgCl surface electrodes (30-mm diameter) were distrib- uted in the direction of the muscle fibers of the VM and VL, in accordance with the method for electrode placement in lower limb muscles for surface electromyographic record- ings described by Rainoldi et al.35 Two additional control electrodes were placed on the medial and lateral tibial pla- teau (Figure 3). The skin under the electrodes was cleaned with a 95% alcohol solution. To assess the muscle performance values, an isokinetic Figure 2. Axial view magnetic resonance imaging showing test (Biodex dynamometer) was performed both presur- the cross-sectional area of the vastus medialis and vastus gically and 6 weeks postsurgically, which provided data lateralis at (A) 3.75 cm and (B) 15 cm from the upper pole of on muscular strength through range of motion at 60 deg/s the patella. (Figure 4). The electrophysiological and isokinetic tests were performed on both knees by the same physical ther- echo time, 11.3 milliseconds; field of view, 17  17 cm; 60 apist, who was blinded to whether the patient had PFP. All patients completed the functional Lysholm knee score partitions; matrix, 448  288 pixels; acquisition time, 2.55 before the operation and at the control visit. This question- minutes). Sagittal images were obtained at a partition thick- naire has been validated in patients with ligamentous,24 ness of 6 mm, with a partition interval of 4.5 mm and an in- chondral,25 and meniscal2,12 injuries as well as in people plane resolution of 0.31 to 0.83 mm. All the MRI assessments with normal or healthy knees.6,7 were performed blinded to patient identification, time sequences, and other knee structural measurements. This measurement was performed at 3.75 cm for the VM and Statistical Analysis 15 cm for the VM and VL from the upper pole of the patella, according to Wang et al45 (Figure 2). The VL/VM ratio was Numerical variables are expressed descriptively as calculated with those values.31 Every MRI measurement means and standard deviations. Within the groups, was performed blinded by 2 independent observers (radiolo- changes (pre- vs postoperative) were evaluated through gists specialized in the musculoskeletal system). paired t tests. This was performed separately for the PFP Likewise, the electrical contractility of the quadriceps group and the control group. Pre- to postoperative differ- femoris was analyzed with surface electromyography ences were calculated for each parameter and for every 4 Amestoy et al The Orthopaedic Journal of Sports Medicine TABLE 1 Muscle Thickness Between the Study Groupsa Cross-sectional Area, cm2 PFP Group Control Group P Value Preoperative VL15cm 21.09 ± 3.55 22.30 ± 3.67 .072 VM15cm 15.79 ± 2.95 17.20 ± 2.66 .127 VM3.75cm 17.66 ± 2.62 19.25 ± 4.01 .081 VL/VM ratiob 1.35 ± 0.21 1.32 ± 0.26 .282 Postoperative VL15cm 15.88 ± 2.47 20.72 ± 3.35 <.001 VM15cm 9.06 ± 2.25 14.92 ± 2.96 <.001 VM3.75cm 9.67 ± 1.84 16.55 ± 3.89 <.001 VL/VM ratiob 1.76 ± 0.25 1.63 ± 0.26 .035 Difference VL15cm 5.11 ± 2.01 1.38 ± 1.67 <.001 VM15cm 6.80 ± 1.96 2.28 ± 1.87 <.001 VM3.75cm 7.80 ± 2.15 2.69 ± 3.18 <.001 VL/VM ratiob 0.77 ± 0.09 0.98 ± 0.13 .022 Figure 3. Electrode placement for surface electromyography a Data are reported as mean ± SD. Bold P values indicate sta- in a left knee. There were 2 electrodes on the vastus medialis, tistically significant difference between groups (P < .05). PFP, 2 on the vastus lateralis, and 2 additional control electrodes patellofemoral pain; VL, vastus lateralis; VM, vastus medialis. b Cross-sectional area ratio. on the bone surface. RESULTS Of the remaining 90 patients after exclusions, 6 were lost to follow-up. The losses included 2 patients from the PFP group and 4 patients from the control group. These follow- up losses were found to be nondifferential for the statisti- cal analysis of the data, because they did not affect the demographics of the 2 groups. Of the remaining 84 patients, 20 (23.80%) were allocated to the PFP group for developing postoperative anterior knee pain, and 64 (76.20%) were considered controls. There were 55 men (65.47%) and 29 women (34.53%), and the mean ± SD age of the sample was 44.92 ± 11.01 years. Both groups were comparable in terms of all the preoperative variables analyzed. Muscle Thickness Figure 4. Isokinetic testing on a Biodex dynamometer. Although the muscle thickness was comparable between the groups preoperatively (Table 1), patients who developed patient. These differences were used to perform PFP showed a greater decrease in muscle thickness between-group comparisons by means of unpaired t (5.11 cm2 for VL15 cm, 6.80 cm2 for VM15cm, and 7.80 cm2 tests. Stata Version 15.1 (StataCorp) was used for statis- for VM3.75cm or VMO) with respect to the control group tical analysis. P <.05 were considered statistically (1.38, 2.28, and 2.69 cm2, respectively) at 6 weeks after significant. surgery (P < .001 for all). A sample-size calculation was made beforehand. Based on an alpha risk of .05, a beta risk of 0.2, and a relative risk of 0.1, a sample of 88 patients was necessary. The propor- Surface Electromyography Results tion of patients who developed PFP after surgery was esti- mated to be 0.25, the same as the incidence in healthy Muscle activity decreased to a greater extent in the PFP people.41 A follow-up loss of 5% was assumed. The Poisson group (804.25 mV in the VL and 1250.80 mV in the VM) than approximation was used. in the control group (486.95 and 680.82 mV) at 6 weeks after the index arthroscopy (P ¼ .036 and P < .001, respectively). The Orthopaedic Journal of Sports Medicine Patellofemoral Pain After Arthroscopy 5 TABLE 2 TABLE 3 Electrical Contractility of the Femoral Quadriceps Between Muscle Strength at 60 deg/s Between the Study Groupsa the Study Groupsa Muscle Strength, kg Muscle Activity, mV PFP Group Control Group P Value PFP Group Control Group P Value Preoperative 23.62 ± 8.57 25.11 ± 9.17 .521 Preoperative Postoperative 12.27 ± 5.59 20.02 ± 5.92 <.001 VL MA 2418.25 ± 940.90 2686.00 ± 984.84 .721 Difference 11.35 ± 6.78 5.09 ± 7.86 <.001 VM MA 2477.10 ± 936.34 2626.93 ± 914.38 .436 VL MVC 266.90 ± 70.82 264.43 ± 115.50 .784 a Data are reported as mean ± SD. Bold P values indicate sta- VM MVC 271.15 ± 80.72 248.93 ± 109.19 .420 tistically significant difference between groups (P < .05). PFP, Postoperative patellofemoral pain. VL MA 1614.00 ± 671.74 2199.05 ± 840.24 .021 VM MA 1226.30 ± 565.79 1946.11 ± 799.33 <.001 VL MVC 159.79 ± 55.94 222.33 ± 63.32 .035 TABLE 4 VM MVC 122.90 ± 63.94 231.75 ± 62.83 <.001 Lysholm Scores Between the Study Groupsa Difference VL MA 804.25 ± 762.82 486.95 ± 421.34 .036 PFP Group Control Group P Value VM MA 1250.80 ± 985.02 680.82 ± 440.32 <.001 Preoperative 59.85 ± 17.14 55.56 ± 14.16 .307 VL MVC 107.11 ± 99.11 42.10 ± 73.40 .008 Postoperative 63.05 ± 14.70 74.45 ± 10.85 <.001 VM MVC 148.25 ± 103.57 17.18 ± 80.44 <.001 Difference 3.2 ± 12.95 18.89 ± 13.34 <.001 a Data are reported as mean ± SD. Bold P values indicate sta- a Data are reported as mean ± SD. Bold P values indicate sta- tistically significant difference between groups (P < .05). MA, mus- tistically significant difference between groups (P < .05). PFP, cle activity; MVC, maximum voluntary contraction; PFP, patellofemoral pain. patellofemoral pain; VL, vastus lateralis; VM, vastus medialis. holistic approach has been attempted for the treatment of The maximum voluntary contraction analysis showed these patients,36 physical therapy continues to focus on results in line with those previously mentioned (Table 2). quadriceps muscle strength to improve patellofemoral tracking and is the most commonly prescribed interven- Isokinetic Testing Results tion.19 However, recent protocols emphasize the impor- tance of some other distant muscles, such as the abductor The preoperative isokinetic study showed muscle strength and external rotators of the hip, in the treatment of anterior data of 23.61 kg in the PFP group and 25.11 kg in the knee pain.22,28 These muscles decrease internal femoral control group (P ¼ .521). It dropped to 12.27 kg in the PFP rotation and excessive functional valgus during patellofe- group and 20.02 kg in the control group (P < .001) at moral tracking and therefore reduce the pressure on the 6 weeks after surgery (Table 3). lateral patellar facet.34 Assuming that postoperative proximity inhibition is Functional Results more noticeable in the thigh than in the gluteus muscle group, the present investigation has focused on the muscles Preoperative Lysholm scores were quite similar (PFP, around the knee.4 In this sense, the results indicate that 59.85; control, 55.56; P ¼ .307). However, in the postoper- patients in whom PFP appears after arthroscopic surgery ative period, the patients who developed PFP had signifi- experience muscular atrophy of the VL and, to a greater cant worse functional results (PFP, 63.05; control, 74.45; extent, the VM. This decrease in quadriceps femoris muscle P < .001) (Table 4). size might be related to the development of PFP. The decreased cross-sectional area of the quadriceps femoris muscle has been reported in patients with PFP as compared DISCUSSION with asymptomatic controls.21 Similar observations have The most important finding of the current investigation is been reported after a total knee arthroplasty. Here, that patients who develop PFP after APM have not only strengthening of the VM optimizes patellar tracking. It is greater loss of muscle thickness but also a greater decrease also associated with lower patellofemoral contact pressure in muscle strength and electrical contractility of the quad- and a reduced contact area. 26 Therefore, simple self- riceps femoris. In that sense, the hypothesis has been rehabilitation with open chain exercises to strengthen the confirmed. quadriceps femoris muscle might be helpful in preventing The cause of anterior knee pain is likely to be multifac- postoperative PFP.26,44 torial with a wider range of factors involved. Neuromuscu- Muscle atrophy is not the only condition these patients lar, anatomic, mechanical, and even psychological experience. They also have a decrease in quadricipital neu- factors13,30,32,38 have all been suggested as causative, which romuscular activity, in as much as the recruitment of mus- explains the unpredictable results of treatment. Although a cle fibers measured by surface electromyography decreases 6 Amestoy et al The Orthopaedic Journal of Sports Medicine considerably as compared with the preoperative values. transverse plane, including increased femoral anteversion Again, this is more in the VM muscle than in the VL mus- and lateral tibial torsion, may contribute to patellofemoral cle. Nevertheless, not all PFP patients demonstrate VM-VL malalignment, and PFP must also be considered.11,14 These dysfunction; this is explained by the normal physiological factors were not analyzed in the current study, so they variability in the healthy population. Arthrogenous quad- might be another limitation. Last, there is the definition riceps muscle inhibition is associated with the severity of of PFP, which is based on the subjective presence of pain the anterior knee pain in patients with patellofemoral joint (or not) in the anterior part of the knee. This is determined osteoarthritis.8 Decreased quadriceps activation has also by self-referral and not by more objective and specific mea- been observed in the acute stage of an ACL injury and in sures or patellofemoral questionnaires, such as the patellar patients with ACL-deficient knees who experience instabil- diagnostic test (Felson test).42 ity (noncopers).23,40 This supports the findings of studies In light of the current results, any neuromuscular def- that obtained better results in the treatment of PFP when icit observed after APM should be monitored and specific neuromuscular control techniques (neuromuscular electri- rehabilitation protocols applied to maintain functional cal stimulation and proprioceptive neuromuscular facilita- stability of the knee to avoid any postoperative dysfunc- tion) were combined with muscle enhancement or tion, such as quadriceps femoris muscle atrophy or loss of strengthening techniques.1,5,30 strength. A trend toward delayed activation of the VMO muscle relative to the VL muscle was seen in those patients with postoperative PFP versus those without. These differences CONCLUSION in the activation of the quadriceps heads during contraction have also been observed among adolescent female patients The results suggest that patients who develop PFP after with PFP when compared with healthy controls.5,9 How- APM have more quadriceps femoris atrophy at 6 weeks ever, this association has not been described in patients after surgery as compared with patients who do not develop with PFP after knee arthroscopy. The delay in VMO muscle this pain. Moreover, they have decreased muscle strength fiber recruitment relative to the VL muscle during func- and electrical contractility of the VM to a greater degree tional activity may adversely affect patellar tracking, thus with respect to the VL. This group of patients also has contributing to the presence of postoperative anterior knee worse functional results after surgery. pain. For this reason, this study confirms the importance of VM in the PFP for the first time. Therefore, the role of the VMO in atrophy at the clinical level, which had been reviled ACKNOWLEDGMENT in recent years to the detriment of the gluteal musculature, is again brought into focus.10 Another interesting finding of The authors thank the radiology department of Hospital del the current work is the incidence of PFP after an arthro- Mar for its help in performing the measurements on the scopic meniscectomy in patients who did not previously magnetic resonance images. They also thank Mr Sanchez have this pain. The 23.8% incidence of postoperative PFP and Ms Piqueras, physical therapists from the INVALCOR is similar to that of patients after ACL reconstruction at 1- Biomechanical Center, who collaborated in the perfor- and 2-year follow-up (24% and 22%, respectively).12 How- mance of all isokinetic and electromyographic tests on our ever, the shorter follow-up time in the present investigation patients. This study was carried out within the framework impedes drawing any sound conclusion on this particular of the doctoral program of the Department of Surgery and issue. Morphological Sciences of the Universitat Autònoma de Intraoperative tourniquet use may be detrimental to the Barcelona. quadriceps femoris after knee surgery. Some studies have demonstrated that tourniquet use resulted in a signifi- cantly decreased thigh circumference as well as significant REFERENCES negative electromyographic changes at 3 weeks after ACL 1. Alba-Martı́n P, Gallego-Izquierdo T, Plaza-Manzano G, Romero-Franco reconstruction.3 In the present study, a tourniquet was N, Núñez-Nagy S, Pecos-Martı́n D. Effectiveness of therapeutic phys- used on all patients regardless of their group. Therefore, ical exercise in the treatment of patellofemoral pain syndrome: a sys- the tourniquet affected both groups equally and was not a tematic review. J Phys Ther Sci. 2015;27(7):2387-2390. confounding factor. 2. Arroyo-Morales M, Martin-Alguacil J, Lozano-Lozano M, et al. The Lysholm score: cross cultural validation and evaluation of psychomet- Some limitations can be found in the present study. First ric properties of the Spanish version. PLoS One. 2019;14(8): is the severity of meniscal damage and consequently the e0221376. amount of meniscus removed at surgery, as it might have 3. Baron JE, Parker EA, Duchman KR, Westermann RW. Perioperative an impact on the degree of postoperative atrophy. Second is and postoperative factors influence quadriceps atrophy and strength the duration of symptoms before surgery and the lack of after ACL reconstruction: a systematic review. Orthop J Sports Med. follow-up after 6 weeks, which make it impossible to ascer- 2020;8(6):232596712093029. tain the evolution of these patients in the medium and long 4. Berry PA, Teichtahl AJ, Galevska-Dimitrovska A, et al. Vastus medialis cross-sectional area is positively associated with patella cartilage and term. However, the aim of the present study was to quan- bone volumes in a pain-free community-based population. Arthritis tify data in a relatively short period after surgery and not to Res Ther. 2008;10(6):R143. ascertain the clinical evolution of these patients in the long 5. Briani RV, De Oliveira Silva D, Flóride CS, et al. Quadriceps neuro- run. Lower extremity structural anomalies on the muscular function in women with patellofemoral pain: influences of The Orthopaedic Journal of Sports Medicine Patellofemoral Pain After Arthroscopy 7 the type of the task and the level of pain. PLoS One. 2018;13(10): 24. Kocher MS, Steadman JR, Briggs K, Zurakowski D, Sterett WI, Haw- e0205553. kins RJ. Determinants of patient satisfaction with outcome after ante- 6. Briggs KK, Kocher MS, Rodkey WG, Steadman JR. Reliability, valid- rior cruciate ligament reconstruction. J Bone Joint Surg Am. 2002; ity, and responsiveness of the Lysholm knee score and Tegner activity 84(9):1560-1572. scale for patients with meniscal injury of the knee. J Bone Joint Surg 25. Kocher MS, Steadman JR, Briggs KK, Sterett WI, Hawkins RJ. Reli- Am. 2006;88(4):698-705. ability, validity, and responsiveness of the Lysholm knee scale for 7. Briggs KK, Steadman JR, Hay CJ, Hines SL. Lysholm score and various chondral disorders of the knee. J Bone Joint Surg Am. Tegner activity level in individuals with normal knees. Am J Sports 2004;86(6):1139-1145. Med. 2009;37(5):898-901. 26. Lin Y-F, Lin J-J, Jan M-H, Wei T-C, Shih H-Y, Cheng C-K. Role of 8. Callaghan MJ, Parkes MJ, Hutchinson CE, Felson DT. Factors asso- the vastus medialis obliquus in repositioning the patella: a dynamic ciated with arthrogenous muscle inhibition in patellofemoral osteoar- computed tomography study. Am J Sports Med. 2008;36(4): thritis. Osteoarthritis Cartilage. 2014;22(6):742-746. 741-746. 9. Carry PM, Kanai S, Miller NH, Polousky JD. Adolescent patellofe- 27. Marcon M, Ciritsis B, Laux C, et al. Cross-sectional area measure- moral pain: a review of evidence for the role of lower extremity ments versus volumetric assessment of the quadriceps femoris mus- biomechanics and core instability. Orthopedics. 2010;33(7): cle in patients with anterior cruciate ligament reconstructions. Eur 498-507. Radiol. 2015;25(2):290-298. 10. Chester R, Smith TO, Sweeting D, Dixon J, Wood S, Song F. The 28. Mascal CL, Landel R, Powers C. Management of patellofemoral pain relative timing of VMO and VL in the aetiology of anterior knee pain: targeting hip, pelvis, and trunk muscle function: 2 case reports. a systematic review and meta-analysis. BMC Musculoskelet Disord. J Orthop Sports Phys Ther. 2003;33(11):647-660. 2008;9:64. 29. Matsusue Y, Thomson NL. Arthroscopic partial medial meniscectomy 11. Cibulka MT, Threlkeld-Watkins J. Patellofemoral pain and asymmet- in patients over 40 years old: a 5- to 11-year follow-up study. Arthros- rical hip rotation. Phys Ther. 2005;85(11):1201-1207. copy. 1996;12(1):39-44. 12. Culvenor AG, Øiestad BE, Holm I, Gunderson RB, Crossley KM, Ris- 30. Pal S, Draper CE, Fredericson M, et al. Patellar maltracking correlates berg MA. Anterior knee pain following anterior cruciate ligament with vastus medialis activation delay in patellofemoral pain patients. reconstruction does not increase the risk of patellofemoral osteoar- Am J Sports Med. 2011;39(3):590-598. thritis at 15- and 20-year follow-ups. Osteoarthritis Cartilage. 2017; 31. Pan J, Stehling C, Muller-Hocker C, et al. Vastus lateralis/vastus med- 25(1):30-33. ialis cross-sectional area ratio impacts presence and degree of knee 13. Doménech J, Sanchis-Alfonso V, Espejo B. Changes in catastrophiz- joint abnormalities and cartilage T2 determined with 3 T MRI—an ing and kinesiophobia are predictive of changes in disability and pain analysis from the incidence cohort of the Osteoarthritis Initiative. after treatment in patients with anterior knee pain. Knee Surg Sports Osteoarthritis Cartilage. 2011;19(1):65-73. Traumatol Arthrosc. 2014;22(10):2295-2300. 32. Pattyn E, Verdonk P, Steyaert A, et al. Vastus medialis obliquus atro- 14. Erkocak OF, Altan E, Altintas M, Turkmen F, Aydin BK, Bayar A. Lower phy: does it exist in patellofemoral pain syndrome? Am J Sports Med. extremity rotational deformities and patellofemoral alignment para- 2011;39(7):1450-1455. meters in patients with anterior knee pain. Knee Surg Sports Trauma- 33. Paxton ES, Stock MV, Brophy RH. Meniscal repair versus partial tol Arthrosc. 2016;24(9):3011-3020. meniscectomy: a systematic review comparing reoperation rates and 15. Goldblatt JP, Fitzsimmons SE, Balk E, Richmond JC. Reconstruc- clinical outcomes. Arthroscopy. 2011;27(9):1275-1288. tion of the anterior cruciate ligament: meta-analysis of patellar ten- 34. Petersen W, Ellermann A, Gösele-Koppenburg A, et al. Patellofemoral don versus hamstring tendon autograft. Arthroscopy. 2005;21(7): pain syndrome. Knee Surg Sports Traumatol Arthrosc. 2014;22(10): 791-803. 2264-2274. 16. Grapar Žargi T, Drobnič M, Vauhnik R, Koder J, Kacin A. Factors 35. Rainoldi A, Melchiorri G, Caruso I. A method for positioning electrodes predicting quadriceps femoris muscle atrophy during the first 12 during surface EMG recordings in lower limb muscles. J Neurosci weeks following anterior cruciate ligament reconstruction. Knee. Methods. 2004;134(1):37-43. 2017;24(2):319-328. 36. Sanchis-Alfonso V. Holistic approach to understanding anterior knee 17. Hart HF, Ackland DC, Pandy MG, Crossley KM. Quadriceps volumes pain: clinical implications. Knee Surg Sports Traumatol Arthrosc. are reduced in people with patellofemoral joint osteoarthritis. Osteo- 2014;22(10):2275-2285. arthritis Cartilage. 2012;20(8):863-868. 37. Sanchis-Alfonso V.Patellofemoral pain. Article in German. Orthopade. 18. Heijden RA, Lankhorst NE, Linschoten R, Bierma-Zeinstra SMA, Mid- 2008;37(9):835-836, 838-840. delkoop M. Exercise for treating patellofemoral pain syndrome. 38. Sanchis-Alfonso V, Roselló-Sastre E. Immunohistochemical analysis Cochrane Database Syst Rev. 2015;1:CD010387. for neural markers of the lateral retinaculum in patients with isolated 19. Hiemstra LA, Kerslake S, Arendt EA. Clinical rehabilitation of symptomatic patellofemoral malalignment: a neuroanatomic basis for anterior knee pain: current concepts. Am J Orthop. 2017;46(2): anterior knee pain in the active young patient. Am J Sports Med. 2000; 82-86. 28(5):725-731. 20. Karaman O, Ayhan E, Kesmezacar H, Seker A, Unlu MC, Aydingoz O. 39. Seil R, Becker R. Time for a paradigm change in meniscal repair: save Rotational malalignment after closed intramedullary nailing of femoral the meniscus! Knee Surg Sports Traumatol Arthrosc. 2016;24(5): shaft fractures and its influence on daily life. Eur J Orthop Surg Trau- 1421-1423. matol. 2014;24(7):1243-1247. 40. Shanbehzadeh S, Mohseni Bandpei MA, Ehsani F. Knee muscle 21. Kaya D, Citaker S, Kerimoglu U, et al. Women with patellofemoral activity during gait in patients with anterior cruciate ligament injury: pain syndrome have quadriceps femoris volume and strength a systematic review of electromyographic studies. Knee Surg Sports deficiency. Knee Surg Sports Traumatol Arthrosc. 2011;19(2): Traumatol Arthrosc. 2017;25(5):1432-1442. 242-247. 41. Smith BE, Selfe J, Thacker D, et al. Incidence and prevalence of 22. Khayambashi K, Mohammadkhani Z, Ghaznavi K, Lyle MA, Powers patellofemoral pain: a systematic review and meta-analysis. PLoS CM. The effects of isolated hip abductor and external rotator muscle One. 2018;13(1):e0190892. strengthening on pain, health status, and hip strength in females with 42. Stefanik JJ, Neogi T, Niu J, et al. The diagnostic performance of patellofemoral pain: a randomized controlled trial. J Orthop Sports anterior knee pain and activity-related pain in identifying knees with Phys Ther. 2012;42(1):22-29. structural damage in the patellofemoral joint: the Multicenter Osteo- 23. Knoll Z, Kocsis L, Kiss RM. Gait patterns before and after anterior arthritis Study. J Rheumatol. 2014;41(8):1695-1702. cruciate ligament reconstruction. Knee Surg Sports Traumatol 43. Stein T, Mehling AP, Welsch F, von Eisenhart-Rothe R, Jäger A. Long- Arthrosc. 2004;12(1):7-14. term outcome after arthroscopic meniscal repair versus arthroscopic 8 Amestoy et al The Orthopaedic Journal of Sports Medicine partial meniscectomy for traumatic meniscal tears. Am J Sports Med. 46. Werner S. Anterior knee pain: an update of physical therapy. Knee 2010;38(8):1542-1548. Surg Sports Traumatol Arthrosc. 2014;22(10):2286-2294. 44. Tang SF, Chen CK, Hsu R, Chou SW, Hong WH, Lew HL. Vastus 47. Wünschel M, Leichtle U, Obloh C, Wülker N, Müller O. The effect of medialis obliquus and vastus lateralis activity in open and closed different quadriceps loading patterns on tibiofemoral joint kinematics kinetic chain exercises in patients with patellofemoral pain syndrome: and patellofemoral contact pressure during simulated partial weight- an electromyographic study. Arch Phys Med Rehabil. 2001;82(10): bearing knee flexion. Knee Surg Sports Traumatol Arthrosc. 2011; 1441-1445. 19(7):1099-1106. 45. Wang Y, Wluka AE, Berry PA, et al. Increase in vastus medialis cross- 48. Yildirim AO, Aksahin E, Sakman B, et al. The effect of rotational sectional area is associated with reduced pain, cartilage loss, and deformity on patellofemoral parameters following the treatment of joint replacement risk in knee osteoarthritis. Arthritis Rheum. 2012; femoral shaft fracture. Arch Orthop Trauma Surg. 2013;133(5): 64(12):3917-3925. 641-648.