Combined Proximal Tibial Osteotomy(CPTO) For Varus Osteoarthritis Of The Knee:Biomechanical Tests And Clinical Evaluation

BACKGRAUND AND PURPUSEKnee osteoarthritis is one of the most common musculoskeletal disorders,especially among the elderly.Advanced knee osteoarthritis is usually accompanied with severe varus deformity.Intra-articular instability is assumed to be a critical factor in advanced knee osteoarthritis.The purpose of the study was to identify intra-articular instability with specialist physical examination and investigate the correlations between the intra-articular instability and the indicators of image examination.Varus deformity of knee osteoarthritis was formed by both intra-articular and extra-articular pathologies.Such intra-articular deformities could not be fully corrected by a medial open-wedge high tibial osteotomy(OWHTO),which was performed as an extra-articular procedure.Therefore,the purpose of this study was to investigate whether any residual varus was left inside the joint after OWHTO in the patients with varus knee osteoarthritis(VKOA),and a correlation of the residual varus could be traced.A special combined proximal tibial osteotomy(CPTO)was designed to treat VKOA with severe intra-articular pathologies,which could not be fully corrected by OWHTO.The biomechanical strength of the CPTO bone-implant construct was evaluated and compared with those of existing osteotomy methods.As a type of high tibial osteotomy for advanced VKOA,the concept of CPTO,the current surgical technique with a locking plate,and the short-term clinical and radiological results of this procedure were reported in the research.SUBJECTS AND METHODS163 patients involving 192 knees were investigated.The intra-articular instability of the knees was checked with physical examination by six orthopaedic surgeons independently in three groups.A radiograph of the full-length leg in a standing position was performed.Kellgren-Lawrence grade was used for classifying the severity of VKOA.The percentage of mechanical axis(%MA),mechanical femorotibial angle(m FTA),mechanical lateral distal femoralangle(m LDFA),mechanical medial proximal tibial angle(m MPTA),joint line convergence angle(JLCA)and medial tibial plateau depression(MTPD)were measured.Weighted kappa was used to determine the inter-reliability and intra-reliability of intra-articular instability.Correlations between each radiographic parameter and the grade of intra-articular instability were assessed using Spearman correlation analysis.The radiographic threshold of intra-articular instability was tested by means of a Chi-square test.This study involved 66 patients(66 knees)undergoing OWHTO for VKOA.The percentage of %MA,m FTA,m LDFA,m MPTA and JLCA were measured on radiographs of the full-length legs preoperatively and 6months postoperatively.The relationship between changes in JLCA and alignment correction was assessed.The postoperative residual JLCA was categorized as the optimal(postoperative JLCA ≤2°),the acceptable(2°<postoperative JLCA≤5°)and the unacceptable(postoperative JLCA>5°)to analyze its correlation with pre-or intra-operative factors.Three variations of osteotomy including OWHTO,tibial condylar valgus osteotomy(TCVO),and CPTO were performed on synthetic bones with locking plate and screws.All three valgus osteotomies were performed to correct the varus tibial plateau to a horizontal position.The plate fixator and locking of proximal screws were later inserted.Wedge stiffness,wedge displacement,and load failure was measured by biomechanical tests.Three types of numerical tibial models were also constructed by 3D model reconstruction software.The stability parameters of the three variations including wedge stiffness,wedge displacement,and stress distribution were further measured by finite-element analyses.23 knees with VKOA and a widened lateral joint were treated by CPTO(KL stage III: 14,IV: 9).In this procedure,an L-shaped osteotomy from the medial side of the proximal tibia to the inter-condylar eminence was performed to obtain the valgus correction,lateralization of the mechanical axis and reduction of intra-articular pathologies.Next,a wedge-shape osteotomy was performed in the lateral of the tibia,leaving a lateral bone bridge of 5 mm as a hinge to correct the extra-articular varus deformity.Then,one more proximal screw was inserted adjacent to the plate fixator and was placed deep enough to reach the lateral part of the tibia.Before,6 months and 1 year after the operation,a visual analog scale(VAS),the Western Ontario and Mc Master Universities Arthritis Index(WOMAC),alignment of the lower extremity,and congruency and stability of the femorotibial joint were investigated.RESULTSThe agreement for intra-articular instability has a substantial inter-reliability and intra-articular reliability ranging from 0.574 to 0.671 and 0.678 to 0.688 respectively.The inter-and intra-rater reliabilities also showed moderate to substantial agreements for each grade of intra-articular instability.Intra-articular instability showed correlate positively with Kellgren-Lawrence grade and intra-articular pathologies including JLCA and MPTD.The threshold of JLCA and MPTD for Grade1 to Grade 2 of intra-articular instability was 2° and 3° respectively and the threshold for Grade 2 to Grade 3 was 5° and 7° respectively.Average %MA and m FTA were improved from 5.5% to 60% and from 190.2° to 176.4°,respectively.There was no change in m LDFA,whereas m MPTA changed from 80.3° to 91.8°.JLCA changed from 4.2° to2.7°.The analyses of multiple linear regression showed that the preoperative JLCA and postoperative changes in mechanical alignment(%MA,m FTA and m MPTA)were two important variables dependently associated with differences in JLCAs postoperatively.However,postoperative JLCAs showed a stronger correlation to preoperative JLCAs than to changes in mechanical alignment postoperatively.A Chi-square analysis showed a significantly higher percentage of patients achieved acceptable postoperative JLCAs in the preoperative JLCA≤6° group(78.8%)compared to the preoperative JLCA>6° group(6.1%).Therefore,6° of JLCA was suggested as a tipping point.The biomechanical testing results revealed that the wedge stiffness,wedge displacement and failure load of the CPTO construct were very close to those of the OWHTO construct.The numerical results of the wedge stiffness and displacement showed good conformity to the previous biomechanical results.The stress distribution at the lateral hinge,the plate corner and the holes of the CPTO construct were close to those of the OWHTO counterpart,while the stress distribution at the inter-condylar eminence of the tibia and at the middle region of the screws was close to those of the TCVO counterpart.The VAS improved from an average of 75.2 mm to 13.8 mm 1 year after operation,and the total WOMAC score from 54.7 to 22.3 before to 1year after the operation,respectively.The %MA changed from 1% to 60%.The m FTA changed from 168.9° to 184.6°.The m MPTA changed from80.1° to 92.5°.The JLCA was relieved from 5.7° to 1.2°,and the MPTD was improved from 7.8° to 5.0° after the operation.No serious complications occurred one year after the operation.CONCLUSIONThe phenomenon of intra-articular instability in VKOA could be observed and diagnosed with physical and radiographic examination.The intra-articular pathology of VKOA,such as the intra-articular incongruency and the inclination of the medial compartment of the proximal tibia,contributed most to the intra-articular instability.The capability of OWHTO to correct intra-articular varus deformities,which was represented by JLCA,was limited.Postoperative residual JLCA correlated primarily to preoperative JLCA values and total alignment correction,while the former accounted for most.A preoperative JLCA of6° was suggested as a tipping point,and a larger value indicated more than5° residual JLCA after the OWHTO.The CPTO construct showed biomechanical performance more comparable to the OWHTO construct than the TCVO construct which owned the optimal biomechanical stability.The CPTO construct using a single plate and an additional screw could form an effective stabilizer to significantly resist the compressive loads,enhance construct stiffness and suppress wedge displacement.It suggested that the CPTO construct could provide comparable strength for early mobilization and rehabilitation as that of the OWHTO construct.For the patients with severe VKOA after the treatment of CPTO,pain was alleviated and daily function of knee joint was improved significantly.The lower limb valgus deformity was also corrected,and tibiofemoral articular surface consistency and knee joint stability were restored.In the short term after CPTO,the fixation of wedge fixation is stable and reliable,and the risk of postoperative complications is relatively low.The efficacy of CPTO remains to be verified with further long-term clinical follow-up.