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Coventry Method of HTO

- Discussion:
    - the Coventry type of HTO, creates an osteotomy above the tibial tubercle;
    - in choosing a closing wedge osteotomy, the surgeon should be sure that the major deformity is on the tibial side (vs femoral side);
    - the disadvantages of this type of osteotomy include possible non union, neurologic injury, and patellar baja;
    - outcomes:
          - in the study by Odenbring et al (1990), 75% of patients under the age of 50 w/ early medial DJD had at good result at 11 years
                 post surgery;
          - in the report by Billings A, et al (1999), 64 valgus producing high tibial osteotomies were performed using a calibrated cutting
                 guide w/ plate fixation;
                 - 43 out of 64 knees had a good to excellent clinical result w/ knee score of 94 points at an average of 8.5 years follow up;
                 - using total knee arthroplasty as an end point, there was 85 % survival at 5 yrs and 53 % at 10 years;
                 - no patient had patella baja postoperatively (the authors fell that early ROM w/ CPM prevented baja);
                 - average initial postoperative correction (and standard deviation) for all knees was to 9.2 ± 3.69 degrees of valgus;
                 - 5 knees were corrected to less than 5 deg of valgus; 3 of them were treated with a subsequent arthroplasty (at twenty-four,
                            sixty-five, and sixty-six months);
                 - 13 knees had lost more than 2 deg of correction at the time of the latest follow-up;
                        - average initial postoperative correction for these knees was to 9.4 ± 4.12 deg (range, 4 to 17 degrees) of valgus;
                        - of knees that lost more than 2 degrees of correction, four subsequently had a total knee arthroplasty.
          - references:
                 - Ten year results of tibial osteotomy for medial gonarthrosis: the influence of overcorrection.
                 - High tibial osteotomy with a calibrated osteotomy guide, rigid internal fixation, and early motion. Long-term follow-up.
                 - Revision after osteotomy for gonarthrosis: a 10-19 year follow up of 314 cases.
                 - Proximal tibial osteotomy in patients who are fifty years old or less. A long-term follow-up study.
                 - High tibial osteotomy. A prospective clinical and roentgenographic review.
                 - Cartilage regeneration after proximal tibial osteotomy for medial gonarthrosis. An arthroscopic, roentgenographic, and histologic study.
                 - Results of proximal tibial osteotomy. The effects of tibiofemoral angle, stance-phase flexion-extension, and medial-plateau force.
                 - Proximal osteotomy of the tibia for the treatment of genu recurvatum in adults.
                 - Factors influencing long-term results in high tibial osteotomy.
                 - Valgus high tibial osteotomy. A long-term follow-up study.
                 - High tibial osteotomy.
                 - A ten- to 15-year follow-up observation of high tibial osteotomy in medial compartment osteoarthrosis.
                 - Proximal tibial osteotomy. A critical long-term study of eighty-seven cases.
                 - Proximal tibial osteotomy. Factors that influence the duration of satisfactory function.
                 - High tibial osteotomy. A prospective clinical and roentgenographic review.
                 - Proximal tibial osteotomy for osteoarthritis with varus deformity. A ten to thirteen-year follow-up study.
                 - Valgus high tibial osteotomy. A long-term follow-up study.
                 - Tibial osteotomy for osteoarthritis of the knee. A five to ten-year follow-up study.
                 - Tibial Osteotomy for the Treatment of Varus Gonarthrosis. Survival and failure analysis to twenty-two years.

- General Concept:
    - incision:
           - inverted L shaped incision;
                 - transverse limb:
                         - is made at the level of the joint line (or just below it);
                         - posteriorly the incision extends just past the fibular head;
                         - anteriorly the incision extends to the patellar tendon;
                 - verticle limb:
                         - extends inferiorly along the lateral crest of the tibia for 10 cm;
           - superiorly, taken care not to injure the patellar tendon;
                 - incise thru the patellar paratenon and bluntly spread beneath the tendon;
                 - during the osteotomy cuts, a spade retractor can be placed just underneath the patellar tendon for protection;
           - incision is carried down to periosteum, and anterior compartment musculature is elevated off the cortical surface;
                 - proximally the incision follows the posterior aspect of biceps tendon inorder to expose the peroneal nerve;
           - distally the incision courses obliquely and horizontally to a point just distal to the tibial tubercle;
           - a Chandler "spade" retractor is placed just anterior to the peroneal nerve and a second Chandler is placed just posterior to the
                  patellar tendon;
    - proximal cut is made 1.5 cm below and horizontal to joint line;
           - proximal cut should avoid transecting the posterior tibial cortex, since it is desirable to have the posterior cortex of the
                  proximal fragment overlap the proximal cortex of the distal fragment;
           - distal cut is usually made 7 mm to 1 cm below the proximal cut;
    - management of fibula:

- Method of Fixation: (controversial);  
    - plate fixation: (procedure of choice)
            - offers early mobilization of knee joint & has shortened rehab time and decreased the incidence
                      of patella infera;
            - advantage: does not require immobilization of the knee;
            - disadvantage: does not allow full wt bearing;
    - staple fixation:

- Post Operative Care:
    - importance of early ROM;
            - w/ closing wedge osteotomy, distance between tubercle and joint line is decreased, decreasing tension on patellar ligament;
            - patellar ligament, fat pad, and retinaculum may contract and scar causing patella baja;
            - Billings A, et al. (2000), no patient had patella baja postoperatively (the authors felt that early ROM w/ CPM prevented baja);
    - neurologic exam:
            - depending on whether or not the peroneal nerve is decompressed and depending on how the fibula is managed (fibular
                    osteotomy vs tib-fib capsular transection), all patients will require an immediate postoperative peroneal nerve examination
                    as well as an examination the next day;
                    - a "delayed peroneal nerve palsy" may have two causes:
                    - in some patients, dense fibrous tissue will firmly anchor the peroneal nerve to the neck of the fibula;
                           - in this situation, postoperative edema in this region may cause nerve compression;
                    - alternatively, a "delayed peroneal nerve palsy" may represent an evolving comartment syndrome (which can be masked
                           if an epidural is used for postoperative anesthesia);
                    - ref: HTO with a calibrated osteotomy guide, rigid internal fixation, and early motion. Long-term follow-up.

- Controversies:

    - management of varus laxity following HTO:
            - this may occur due to relative shortening of the femoral to fibular head distance, causing laxity of the LCL;
                   - patients w/ a prominent varus thrust may be especially at risk for postop laxity;
            - when recognized intraoperatively, consider posterolateral advancement;
            - w/ excessive external rotation, then consider advancement of the popliteus;
            - w/ excessive varus laxity, consider advancement of the LCL;
            - both the popliteus and LCL may be advanced together using a common wafer of bone;
    - references:
            - Recurrent Varus Angulation After High Tibial Osteotomy: An Anatomic Analysis.