A retrospective analysis was performed of patients who had undergone an OWHTO-B for symptomatic medial osteoarthritis between 2012 and 2014 at the authors’ institution. Patients who did not have the corresponding radiographies before surgery, immediately after surgery and 24 months after the index procedure were also excluded. All the radiographic studies had to be performed at the index institution.
Like for every tibial osteotomy, the general indications for surgery were the presence of a varus tibial deformity associated with symptomatic narrowing of the medial compartment space, the absence of a flexion contracture, a flexion range of motion of at least 90° and the failure of other conservative treatment. OWHTO-B was particularly indicated when possibility of postoperative Caton Deschamp Index (CDI) less than 0.8 was present due to the risk of excessive and somehow unpredictable degree of patellar lowering: 1) in cases of a CDI less than 0.8, 2) in cases of CDI between 0.8 and 1, but a planned correction greater than 10° and, as extended indication, 3) in case of combined varus malalignment and patellofemoral pain or radiological patellofemoral alterations with a normal CDI. This is due to its ability to decrease the patellofemoral joint pressures (Kloos et al. 2018).
Contraindications were severe bone loss in the femoral condyle or tibial plateau, the presence of rheumatoid arthritis or infectious arthritis, the presence of prominent osteoarthritis in the lateral compartment and markedly limited joint motion.
The clinical research ethics committee of our institution approved the study (protocol number HTOL 2017–01). All the patients signed informed consent to participate in the study as well as for the evaluation and publication of their results.
Preoperative study
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Full-weight-bearing long-leg standing anteroposterior radiographs were performed to determine the angle of the extremity and the desired degree of correction. A postoperative anatomic femoral-tibial axis of 5–8° valgus and a mechanical axis around the Fujisawa point was the goal (Habata et al. 2006).
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The Schuss or Rosenberg radiographic view (Rosenberg et al. 1988) was used to evaluate the joint line space.
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A lateral non-weight-bearing radiography of the knee at 30° of flexion was used to measure the posterior tibial slope and the patellar height. The angle of the posterior tibial slope was determined based on a line passing through the posterior cortex of the tibia and another parallel to the joint slope (Brazier et al. 1996). For patellar height, the CDI was measured as previously described (Caton et al. 1982) (Fig. 1).
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A Merchant view (skyline view with knee flexed to 45°) was used to calculate the lateral patellar tilt (LPT) and the severity of patellofemoral arthritis. 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, performed 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 gracilis 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 performed posterior to the tibial tubercle. Under fluoroscopic 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 maintain perfect perpendicularity to the main axis of the bone on the sagittal plane to avoid tibial slope modifications. This section of the osteotomy ended 1 to 2 cm medial to the lateral border of the tibia. The second section of the osteotomy was vertical in the coronal plane and extended 3 to 4 cm distally. Thus, the TT together with the proximal segment of the osteotomized tibia was maintained. A thickness of 10 mm of the TT should be maintained in the most proximal part to minimize the risk of fracture. The desired correction is achieved using a metallic wedge introduced in the posterior-most part of the osteotomy site, thereby creating a trapezoidal gap to avoid an increase in the tibial slope (Fig. 3). To prevent anterior tilting of the TT leading 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, the locking LOQTEQ®HTO plate (Berlin, Germany), was accordingly fixed (Fig. 4). Finally, the osteotomy gap was filled with an iliac crest allograft.
Rehabilitation protocol
Patients started continuous passive motion of the knee as well as isometric quadriceps strengthening exercises immediately after surgery. During the first 3 weeks, patients were only allowed toe-touch partial weight-bearing. Then, progressive weight bearing as tolerated started. Full weight bearing was allowed after week 6.
Complications were recorded during the study period, which had a minimum follow-up of 24 months.
The same preoperative radiological studies were carried out at the latest follow up.
Clinical assessment
Clinical and functional follow-up included the Lysholm, Kujala and Hospital for Special Surgery (HSS) knee scores. The physical examination as well as the functional evaluation of every patient was performed preoperatively and at final follow-up by a single sports medicine surgeon who was independent of the study. Attention was paid to the clinical evaluation of any postoperative patellofemoral pain manifested by patients.
Radiological follow up
In every case a standard X-ray protocol was obtained preoperative and at 1–6–12-24 months postoperative. 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 Merchant view. Femoral-tibial angle, posterior tibial slope, CDI, LPT and degree of patellofemoral arthritic degeneration were collected. Immediately postoperative was not obviously possible to obtain a full-weight-bearing long-leg standing X-ray as well as a Merchant view. Only standard anteroposterior and lateral non-weight-bearing radiography of the knee at 30° of flexion were obtained.
CDI and posterior tibial slope were collected starting from the immediate postoperative radiographs.
LPT, femoral-tibial angle and severity of patella-femoral arthritis were collected starting from the 1-month follow-up radiographs.
Statistical analysis
Continuous variables are presented as means, standard deviations (SD), maximums and minimums. Categorical variables are presented as percentages and frequencies.
For analysis of the repeated measures, Bonferroni’s correction was used to identify differences between baseline and follow-up radiographic measurements.
Because of the small sample number, statistical tests were not utilized to evaluate normality. Instead, the assessment was performed with non-parametric equivalents, which showed no discrepancies in terms of significance. The inference in continuous variables was calculated with the paired-samples T-test and their results are presented with their 95% confidence interval (95% CI). Interobserver variability was analyzed with the variance test. The level of significance was set at 5% (α = 0.05), a bilateral approximation. All the analyses were performed with the SPSS 19 (SPSS Inc., Chicago, Illinois).