Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 https://doi.org/10.1186/s40634-019-0176-6 Journal of Experimental Orthopaedics RESEARCH Open Access Biplane opening wedge high tibial osteotomy with a distal tuberosity osteotomy, radiological and clinical analysis with minimum follow-up of 2 years Juan Erquicia1, Pablo Eduardo Gelber 1,2, Simone Perelli1* , Federico Ibañez1, Maximiliano Ibañez1, Xavier Pelfort1,3 and Juan Carlos Monllau1,4 Abstract Background: High tibial osteotomy is an established and helpful treatment for unicompatimental osteoarthritis associated with varus deformity. However, asupratubercle high tibial osteotomy leads to a decrease in patellar height making the technique not suitable in case of concomitant patella baja. Moreover, this kind of osteotomy can change in situ forces at patellofemoral joint and the lateral patellar tilt. With the aim to widen the indication of high tibial osteotomy was proposed a biplane opening wedge high tibial osteotomy with a distal tuberosity osteotomy (B-OWHTO). This technique provide that the tibial tuberosity remains joined to the tibial metaphysis so as not to theoretically alter the patellar height. However, some Authors claim that BOWHTO could lead to an increase in tibial slope. The purpose of the present study was to assess the tibial slope, patella-femoral changes and axial correction as well as functional outcomes following a B-OWHTO. Methods: Patients operated on with a B-OWHTO and a minimum 24 months of follow-up were included. The mechanical alignment of the lower limb, patellar height, lateral patellar tilt and posterior tibial slope were calculated preoperatively, immediately after surgery and at the 24-month follow-up. The clinical results were evaluated using the Lysholm, Kujala and Hospital for Special Surgery knee scores. The possible postoperative development of patellofemoral pain or radiologic patellofemoral alteration was also evaluated. Results: Twenty-three patients were included with a mean follow-up of 33 months (range 27-41). The mechanical alignment of the lower limb shifted from a mean 9.3º ± 2.5 varus preoperatively to a mean 0.2º ± 2.2 valgus postoperatively. No changes in patellar height, lateral patellar tilt or in the posterior tibial slope were observed. The mean Lysholm and HSS scores improved from 68.3 ± 9.1 and 64.2 ± 5.2 preoperatively to 93.2 ± 2.1 and 94.1 ± 3.6 at final follow-up (p < 0.01). The mean Kujala score improved from 67.3 ± 9.8 to 86.4 ± 7.6 at final follow up (p < 0.01). No patients developed both radiological or clinical symptoms at patellofemoral joint. Conclusions: Open wedge high tibial osteotomy with a dihedral L-cut distal and posterior to the tibial tubercle accurately corrected axial malalignment without any change at patella-femoral joint or any modification to the posterior tibial slope while providing improved knee function at short-term follow-up. The radiographic as well as the clinical results support the use of this technique to treat medial compartment knee osteoarthritis and varus malalignment in young and middle-aged patients with a normal-to-low patellar height. (Continued on next page) * Correspondence: perelli.simone@gmail.com 1 ICATME, Hospital Universitari Dexeus, UAB, Carrer de Sabino Arana, 5, Barcelona 08028, Spain Full list of author information is available at the end of the article © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 2 of 9 (Continued from previous page) Level of evidence: Case series with no comparison group, Level IV. Keywords: High tibial osteotomy, Open wedge tibial osteotomy, Biplanar tibial osteotomy, Tuberosity osteotomy, Patellar height, Tibial slope Background slope (Akizuki et al. 2008). Increasing the tibial slope High tibial osteotomy (HTO) is an established treatment may affect antero-posterior translation of the tibia as for patients with medial compartment knee osteoarth- well as the in-situ forces on the anterior cruciate ritis (OA) and varus malalignment (Poignard et al. ligament. 2010). Open wedge high tibial osteotomy (OWHTO) has With the aim of solving these potential problems gained in popularity over recent years as a viable alterna- and so broaden OWHTO indications, some authors tive to the traditional lateral closed wedge osteotomy. still support the use of the standard infra-tubercle This technique has several advantages over the lateral HTO in these cases (Shim et al. 2013). However, closed wedge osteotomy. They include avoiding a fibular moving the tibial osteotomy distally reduces the total osteotomy and the risk of peroneal nerve complications surface of cancellous bone at the osteotomy site and (Gaasbeek et al. 2010), smaller surgical exposure without increases the risk of non-union. Several authors have muscle detachment, easier and more precise correction already reported superior clinical outcomes of that can be change even after the osteotomy cut (Bito et traditional supra-tubercle OWHTO over infra al. 2009; Hankemeier et al. 2010). Furthermore, it can -tubercle HTO due to lower non-union rates (Noyes make an eventual future knee replacement easier not et al. 2006). only due to the location of the skin approach but more The further solution suggested by some authors in because an OWHTO decreases the metaphyseal deform- previous studies to deal with these issues is to perform a ity caused by a closed wedge (Hui et al. 2011). modification of the standard technique: a biplane However, OWHTO has some potential disadvan- OWHTO with a distal tuberosity osteotomy (OWH- tages for the patellofemoral joint. Firstly, because a TO-B). This technique provide that the tibial tuberosity supra-tubercle osteotomy can lower the height of the remains joined to the tibial metaphysis so as not to the- patella, which is particularly true when a large correc- oretically alter the patellar height without increasing the tion is required (Amzallag et al. 2013). As a conse- patellofemoral pressions (28) or even diminishing them quence, the use of an OWHTO is not usually (Kloos et al. 2018). recommended in cases of patella infera. (Schallberger The aim of this study was then to assess the tibial et al. 2011; Lobenhoffer et al. 2009) However, it slope, any patello-femoral change and axial correction as should be kept in mind that the origin of patella well as functional outcomes following a OWHTO-B. It infera is likely multifactorial and so even patients was hypothesized that while providing good clinical re- with a preoperative normal-to-low patellar height sults, this technique would accurately correct the axial could end up with this condition. Additionally, malalignment without producing patello-femoral radio- OWHTO can increase patellofemoral contact pressure logical alterations and keeping the posterior tibial slope and cause patellofemoral degeneration overtime even unchanged. when patellar height has not been modified. (Stoffel et al. 2007) For those reasons, some surgeons advise Methods against OWHTO when patellofemoral pain or patello- A retrospective analysis was performed of patients who femoral chondral alterations are present even in pa- had undergone an OWHTO-B for symptomatic medial tients with normal patellar height (Il et al. 2017; Kim osteoarthritis between 2012 and 2014 at the authors’ in- et al. 2016; Kloos et al. 2018). A study recently has stitution. Patients who did not have the corresponding shown that an alteration of the axial alignment of the radiographies before surgery, immediately after surgery patella with a change of the lateral patellar tilt can be and 24 months after the index procedure were also ex- observed with a standard OWHTO. This fact could cluded. All the radiographic studies had to be performed contribute to explaining the changes described before at the index institution. (Lee et al. 2016). Like for every tibial osteotomy, the general indications A second possible drawback of supra-tubercle for surgery were the presence of a varus tibial deformity OWHTO is its tendency to increase the sagittal tibial associated with symptomatic narrowing of the medial Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 3 of 9 compartment space, the absence of a flexion contracture, Preoperative study a flexion range of motion of at least 90° and the failure of other conservative treatment. OWHTO-B was par-  Full-weight-bearing long-leg standing anteroposterior ticularly indicated when possibility of postoperative radiographs were performed to determine the angle of Caton Deschamp Index (CDI) less than 0.8 was the extremity and the desired degree of correction. A present due to the risk of excessive and somehow un- postoperative anatomic femoral-tibial axis of 5–8° predictable degree of patellar lowering: 1) in cases of valgus and a mechanical axis around the Fujisawa a CDI less than 0.8, 2) in cases of CDI between 0.8 point was the goal (Habata et al. 2006). and 1, but a planned correction greater than 10° and,  The Schuss or Rosenberg radiographic view as extended indication, 3) in case of combined varus (Rosenberg et al. 1988) was used to evaluate the malalignment and patellofemoral pain or radiological joint line space. patellofemoral alterations with a normal CDI. This is  A lateral non-weight-bearing radiography of the due to its ability to decrease the patellofemoral joint knee at 30° of flexion was used to measure the pressures (Kloos et al. 2018). posterior tibial slope and the patellar height. The Contraindications were severe bone loss in the fem- angle of the posterior tibial slope was determined oral condyle or tibial plateau, the presence of based on a line passing through the posterior cortex rheumatoid arthritis or infectious arthritis, the pres- of the tibia and another parallel to the joint slope ence of prominent osteoarthritis in the lateral com- (Brazier et al. 1996). For patellar height, the CDI partment and markedly limited joint motion. was measured as previously described (Caton et al. The clinical research ethics committee of our insti- 1982) (Fig. 1). tution approved the study (protocol number HTOL  A Merchant view (skyline view with knee flexed to 2017–01). All the patients signed informed consent to 45°) was used to calculate the lateral patellar tilt participate in the study as well as for the evaluation (LPT) and the severity of patellofemoral arthritis. and publication of their results. The latter was classified into 4 stages according to Merchant et al. (Kim and Joo 2012) (Fig. 2) Two observers, blind from the aim of the study, per- formed all the radiographic measurements. They were carried out using the PACS system (Centricity Enterprise Web V3.0; GE Healthcare). Surgical technique Two senior surgeons performed all the procedures. Once an arthroscopic evaluation of the knee had been done, a 6–7 cm-longitudinal approach mid-way between the tibial tuberosity (TT) and the posteromedial border of the tibia was performed. The semitendinosus and gra- cilis tendons were released and the superficial medial collateral ligament was freed from its distal insertion. The patellar tendon was identified and protected with a retractor. Osteotomy The OWHTO-B has two different osteotomy planes. While the horizontal cut is similar to the standard OWHTO, the vertical part of the osteotomy is per- formed posterior to the tibial tubercle. Under fluoro- scopic control, one 2.4-mm guiding Kirschner wire was placed in the medial cortex of the tibia at the metaphyseal-diaphyseal transition zone with the aim of tipping the fibular head in a proximal and posterolateral direction. The K-wire guided the sagittal cut performed in the posterior two thirds of the tibia. It is crucial to Fig. 1 Measurement of the Caton-Deschamps index and the maintain perfect perpendicularity to the main axis of the posterior tibial slope. CDI: Caton- Deschamps index, TS: tibial slope bone on the sagittal plane to avoid tibial slope Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 4 of 9 Fig. 2 Measurement of the Lateral Patellar Tilt modifications. This section of the osteotomy ended 1 to The same preoperative radiological studies were car- 2 cm medial to the lateral border of the tibia. The sec- ried out at the latest follow up. ond section of the osteotomy was vertical in the coronal plane and extended 3 to 4 cm distally. Thus, the TT to- Clinical assessment gether with the proximal segment of the osteotomized Clinical and functional follow-up included the Lysholm, tibia was maintained. A thickness of 10 mm of the TT Kujala and Hospital for Special Surgery (HSS) knee should be maintained in the most proximal part to scores. The physical examination as well as the func- minimize the risk of fracture. The desired correction is tional evaluation of every patient was performed pre- achieved using a metallic wedge introduced in the operatively and at final follow-up by a single sports posterior-most part of the osteotomy site, thereby creat- medicine surgeon who was independent of the study. ing a trapezoidal gap to avoid an increase in the tibial Attention was paid to the clinical evaluation of any post- slope (Fig. 3). To prevent anterior tilting of the TT lead- operative patellofemoral pain manifested by patients. ing to an increase in the posterior tibial slope, one or two anteroposterior cortical screws fixing the TT were secured before the osteotomy plate was placed. Then, Radiological follow up the locking LOQTEQ®HTO plate (Berlin, Germany), was In every case a standard X-ray protocol was obtained accordingly fixed (Fig. 4). Finally, the osteotomy gap was preoperative and at 1–6–12-24 months postoperative. filled with an iliac crest allograft. The protocol comprised a full-weight-bearing long-leg standing anteroposterior radiographs, a lateral non-weight- bearing radiography of the knee at 30° of flexion, a Mer- Rehabilitation protocol chant view. Femoral-tibial angle, posterior tibial slope, CDI, Patients started continuous passive motion of the knee as LPT and degree of patellofemoral arthritic degeneration well as isometric quadriceps strengthening exercises im- were collected. Immediately postoperative was not obvi- mediately after surgery. During the first 3 weeks, patients ously possible to obtain a full-weight-bearing long-leg were only allowed toe-touch partial weight-bearing. Then, standing X-ray as well as a Merchant view. Only standard progressive weight bearing as tolerated started. Full weight anteroposterior and lateral non-weight-bearing radiography bearing was allowed after week 6. of the knee at 30° of flexion were obtained. Complications were recorded during the study period, CDI and posterior tibial slope were collected starting which had a minimum follow-up of 24 months. from the immediate postoperative radiographs. Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 5 of 9 Fig. 3 Graduated wedge at the level of the posterior tibial cortex LPT, femoral-tibial angle and severity of patella-fem- significance. The inference in continuous variables was oral arthritis were collected starting from the 1-month calculated with the paired-samples T-test and their re- follow-up radiographs. sults are presented with their 95% confidence interval (95% CI). Interobserver variability was analyzed with the Statistical analysis variance test. The level of significance was set at 5% (α = Continuous variables are presented as means, standard 0.05), a bilateral approximation. All the analyses were per- deviations (SD), maximums and minimums. Categorical formed with the SPSS 19 (SPSS Inc., Chicago, Illinois). variables are presented as percentages and frequencies. For analysis of the repeated measures, Bonferroni’s Results correction was used to identify differences between base- During the studied period 33 L-OWHTO were performed. line and follow-up radiographic measurements. Ten patients were excluded because some of the necessary Because of the small sample number, statistical tests postoperative images were lacking. Twenty-three patients were not utilized to evaluate normality. Instead, the as- (15 males and 8 females) with a mean age of 42.7 years sessment was performed with non-parametric equiva- (range 20.1 to 54.3 years) were finally included. The me- lents, which showed no discrepancies in terms of dian body mass index was 27.4 (range of 21.6–32.7). The Fig. 4 Postoperative aspect, without significant modifications in patellar height or the posterior tibial slope Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 6 of 9 mean follow up was 33 months (range 27–41) Concomi- without causing any patellofemoral change or increasing tant surgical procedures were: 1 anterior cruciate ligament the posterior tibial slope. The patients also had im- reconstruction (4.3%), 8 meniscectomy (34.7%), 4 micro- proved outcomes in the evaluated functional outcomes. fractures at medial condyle (17.4%). All these findings confirmed our hypothesis. The rate of complication was low and all the osteotomies healed Radiological assessment without delayed union. The mechanical alignment of the lower limb shifted from Traditional OWHTO techniques cause distalization a mean varus of 9.3° ± 2.5 preoperatively to a mean valgus and lateralization of the TT, resulting in a decrease of of 0.2° ± 2.2 four weeks after surgery and to a mean valgus patellar height as suggested by Goutallier using a math- of 0.4° ± 2.6 at the 24-month follow-up assessment (Table ematical model (Goutallier et al. 1979). In a recent study, 1). The osteotomy did not alter neither the posterior tibial Amzallag et al. showed that patellar height decreased slope nor the patellar height in the immediate postopera- more than 20% in one-third of patients after an tive radiography (Table 1 and Figs. 5 and 6). No differ- OWHTO. (Amzallag et al. 2013) ences were noted neither in lateral patellar tilt at 1-month These changes would negatively affect the functional postoperative X-ray (Table 1). All these parameters results of the osteotomy. Likewise, several recent studies remained unchanged at the 24-month follow-up (Table 1). confirmed the advantages of the closed-wedge HTO Radiographically, most of the patellofemoral joints (20 out over the OWHTO in relation to patellar height preser- of 23) were graded I or II in the Merchant stage system. vation (Bin et al. 2016; Gaasbeek et al. 2004; El-Amrani Merchant grades of the patellofemoral joints were not sig- et al. 2010; Ozel et al. 2015; Brinkman et al. 2008; Noyes nificantly different at preoperative evaluation and at latest et al. 2005; Stoffel et al. 2007; Ferner et al. 2018). This is follow up. There were no differences in the measures cal- even more important in higher axial deviations as a cor- culated for the two observers. relation between the degree of axial correction and the lowering of the patella has been shown (Amzallag et al. Clinical results 2013). With the OWHTO-B technique, the tibial tuber- The mean Lysholm and HSS scores improved from 68.3 osity remains attached to the proximal fragment of the ± 9.1 and 64.2 ± 5.2 preoperatively to 93.2 ± 2.1 and 94.1 osteotomy. Subsequently, the patellar height remained ± 3.6 at final follow-up (p < 0.01). The mean Kujala score unchanged. The OWHTO-B is not intended to increase improved from 67.3 ± 9.8 to 86.4 ± 7.6 at final follow up patellar height as it does not move the patella upwards. (p < 0.01). Preoperatively 5 out of 23 patients reported Therefore, this technique is not recommended in cases mild patellofemoral pain, at the final follow up no pa- of a Caton Deschamp Index less than 0.6. Instead, a tients complained about anterior knee pain. combined HTO and a separate osteotomy of the TT to Only 2 out of the 23 patients included in the study heighten the tuberosity is indicated to handle the varus showed complications. One patient had a pulmonary deformity and the patellar height. thromboembolism. This patient had had similar episode Other authors have already shown some similar modi- two decades before. It was successfully treated with oral fications to the traditional OWHTO technique in order anticoagulants. Another patient required hardware re- to avoid modifications of patellar height. Gaasbeek et al. moval 28 months after surgery. No problems relative to (Gaasbeek et al. 2004), in a study with 17 patients, unions or infections were observed. showed the results of an OWHTO preserving the TT at- tached to the proximal tibia and also fixing the TT with Discussion an anteroposterior screw. However, the authors did so The most important finding of the present study was after the osteotomy plate was fixed. Then, this antero- that a OWHTO-B accurately corrected varus axial mala- posterior screw could not have prevented any eventual lignment in patients with mid-to-low patellar height anterior tilting of the proximal fragment. In addition, the Table 1 Statistical analyses between preoperative and final follow-up results Preoperative Postoperative 24 months Comparison of Comparison of preop Comparison of postop mean score ± SD mean score ± SD postoperative preop and postop and 24 months postop and 24 months postop mean score ± SD (P value) (P value) (P value) Mechanical axis 9.2° ± 2.5° −0.2° ± 2.2° −0.4° ± 2.6° < 0.001 < 0.001 NS Patellar height 0.94 ± 0.1 0.95 ± 0.08 0.95 ± 0.12 NS NS NS Tibial slope 4.4° ± 2.1° 5.1° ± 1.4° 5.2° ± 1.4° NS NS NS Lateral Patellar Tilt 13.1° ± 2.9° 12.9° ± 3.2° 12.8° ± 3.7° NS NS NS SD standard deviation, NS not significant Postoperative score is intended as immediate postoperative for patellar height and posterior tibial slope and 1-month follow-up for tibial slope ant lateral patellar tilt Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 7 of 9 Fig. 5 Pre- and postoperative Caton-Deschamps indexes authors did not measure the tibial slope changes. They the possibility of delayed union, they suggested the use also had two complications. One of the patients had a of this technique only for those patients with an open fracture of the TT and another patient had a delayed physis and/or require minor corrections, have a body union. Conversely, no complications related to the tech- mass index below 25 and that the osteotomy gap be nique were observed in the current study. It is likely that filled with autogenous iliac crest bone graft. the difference in the sequencing of the osteotomy’s fix- Standard OWHTO is contraindicated in patients with ation provided better contact between the tibial tuberos- patella infera. The Caton-Deschamps index defines pa- ity and the distal tibial fragment. tella baja as those between 0.6 and 0.8. Those below 0.6 To avoid modifications in patellar height and the tibial are considered a patella infera. However, there is no con- slope, Shim et al. (Shim et al. 2013) analyzed the results sensus on its threshold in terms of deciding whether to of an OWHTO distal to the TT. Despite achieving ac- perform the OWHTO as the procedure itself decreases ceptable clinical and radiological results and because of patellar height. In a retrospective level IV evidence study Fig. 6 Pre- and postoperative tibial slopes Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 8 of 9 of patients operated on with an OWHTO, El Amrani et slope might alter in situ cruciate ligament forces and in- al. (El-Amrani et al. 2010) observed that the worse func- fluence knee stability (Ozel et al. 2015). Changes to the tional results were associated with postoperative patella tibial slope might also accelerate the process of joint de- infera. Gaasbeek et al. (Gaasbeek et al. 2004) also found generation due to alterations in knee kinematics and a significant reduction in the CDI after OWHTO. All biomechanics as it leads to higher tibiofemoral contact the patients showed lowering of the patella after the pressure on the anterior portion of the tibial plateau and osteotomy and a direct correlation was found between decreased pressure on the posterior femoral condyle the degree of wedge opening and the decrease in patellar (Brinkman et al. 2008). height. In the present study, the OWHTO-B was per- To maintain the posterior slope, it is suggested that formed when possibility of postoperative CDI less than the anterior opening of the osteotomy site should be half 0.8 was present due to the risk of excessive and some- of the posterior opening of the wedge (Noyes et al. how unpredictable degree of patellar lowering. 2005). The current technique, on the other hand, avoids Kim et al., using an SPET/TC evaluation, have shown any increment in the tibial slope by creating a trapez- that an increased signal activity around the patellofe- oidal gap and first fixing the TT with an anteroposterior moral joint was present after an OWHTO even when a screw. low decrease of postoperative Blackburne-Peel ratio was The main limitation of this study was the low number found (Kim et al. 2016). Kim et al. reported that 21.9% of patients and the lack of control group. However, it is of the patients developed patellar OA and 41.2% devel- the largest reported series on such technique. Another oped a trochlear OA after OWHTO. Their findings were limitation is that the short follow-up did not allow for based on a second look arthroscopy made at 21 to 32 the assessment long-term functional and radiological months of follow-up (Il et al. 2017). The prominent find- outcomes. Notwithstanding, the purpose of the investi- ing was that no correlation of this evolution with patellar gation was to rule out any immediate radiological flaws height was found. The conclusion could be that even of this relatively new technique. when the patellar height has not been changed, alter- For that reason, we excluded patients with an incom- ations in patellofemoral pressure forces happen after a plete postoperative radiographic evaluation. However, OWHTO. That is also supported by a recent cadaveric the latter could be considered as a selection BIAS. biomechanical study (Kloos et al. 2018). In any case we must take into account that always a large deformity Conclusions correction in medial open-wedge high tibial osteotomy Biplane OWHTO with a distal tuberosity osteotomy ac- may cause a degeneration of patellofemoral cartilage. curately corrected axial malalignment without changing (Otakara et al. 2019) in the present study an arthro- patellar femoral height, lateral patellar tilt or the poster- scopic second look wasn’t provide, but Kim in his study ior tibial slope while providing improved knee function showed as well that 11.4% of the cases had postoperative at short-term follow-up. anterior knee pain and among them all showed pro- Abbreviations gressed OA on second look arthroscopy. Postoperative CDI: Caton Deschamp Index; HSS: Hospital for Special Surgery; HTO: High anterior knee pain was related to the ICRS grade of the tibial osteotomy; LPT: Lateral patellar tilt; OA: Osteoarthritis; OWHTO: Open patellofemoral joint at the time of second-look arthros- wedge high tibial osteotomy; OWHTO-B: Biplane opening wedge high tibial osteotomy with a distal tuberosity osteotomy; SD: Standard deviation; copy. In our study no patients complained about patello- TT: Tibial tubercle femoral pain at the last follow up, neither the patients who reported patello-femoral discomfort before surgery. Acknowledgements We would like to thank Mr. Eric L. Goode for his help with the English Finally, in their OWHTO series, Lee et al. have shown correction and Mr. Felip A. Montobbio for his work in the illustration process. postoperative statistically significant changes in lateral patellar tilt (Lee et al. 2016). Even if they reported that Authors’ contributions All authors read and approved the final manuscript. this data has no clinical impact at 2 years follow-up, this mechanical alteration could as well explain patellofe- Ethics approval and consent to participate moral cartilage subclinical alteration and patellofemoral All procedures performed in the present study were in accordance with the ethical standards of the institutional research committee and with the 1964 pain at a longer term follow up. In the present study no Helsinki declaration and its later amendments or comparable ethical significant alterations in postoperative lateral patellar tilt standards. was detected at minimum 24 months follow up. Consent for publication Several studies have shown that HTO might result in Informed consent was obtained from all individual participants included in tibial slope changes. (Lu et al. 2018; Wu et al. 2017) in the study. general, the posterior tibial slope increases after Competing interests open-wedge high tibial osteotomies and decreases after On behalf of all authors, the corresponding author states that there is no the closed-wedge procedures. The increase in the tibial conflict of interest. Erquicia et al. Journal of Experimental Orthopaedics (2019) 6:10 Page 9 of 9 Publisher’s Note Kim TW, Kim BK, Kim DW, Sim JA, Lee BK, Lee YS (2016) The SPECT/CT evaluation Springer Nature remains neutral with regard to jurisdictional claims in of compartmental Changesafter open wedge high Tibial osteotomy. Knee published maps and institutional affiliations. Surg Relat Res 28:263–269 Kim YM, Joo YB (2012) Patellofemoral osteoarthritis. Knee Surg Relat Res 24:193– Author details 200 1 ICATME, Hospital Universitari Dexeus, UAB, Carrer de Sabino Arana, 5, Kloos F, Becher C, Fleischer B, Feucht MJ, Hohloch L, Südkamp N, Niemeyer P, Barcelona 08028, Spain. 2Department of Orthopaedic Surgery, Hospital de la Bode G. (2018) High tibial osteotomy increases patellofemoral pressure if Sta Creu i Sant Pau, UAB, Carrer de Sant Quintí, 89, Barcelona 08026, Spain. adverted proximal, while open-wedge HTO with distal biplanar osteotomy 3 Department of Orthopaedic Surgery, Consorci Sanitari de l’Anoia, Hospital discharges the patellofemoral joint: different open-wedge high tibial de Igualada, Av. Catalunya, 11, Barcelona, Spain. 4Department of Orthopaedic osteotomies compared to an extra-articular unloading device. Knee Surg Surgery, Hospital del Mar. Universitat Autònoma de Barcelona (UAB), Passeig Sports Traumatol Arthrosc. 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