SCIENTIFIC PAPER Primary total knee replacement ...

Hong Kong Journal of Orthopaedic Surgery 2002;6(2):65-68.

Primary CCK in severe varus knee

SCIENTIFIC PAPER Primary total knee replacement using constrained condylar prosthesis in knee with severe varus deformity Cheung KW, Yung SHP, Chiu KH Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong.

ABSTRACT Constrained condylar knee prosthesis is commonly used in revision total knee replacement because of ligamentous imbalance. The use of constrained condylar knee prosthesis in primary total knee replacement has not been widely studied, especially in severe varus deformity of the knee. We aim to study the results of primary total knee replacement in knees with severe varus deformity. From 1996 to 1999, we performed 13 constrained condylar knee procedures in 12 patients with varus deformity of greater than 20° . The decision to use constrained condylar knee was determined intraoperatively, principally when the lateral collateral ligament laxity was >2 mm even after adequate medial soft tissue release. The average follow-up was 38.9 months. The mean varus deformity was 24.6°. The Knee Society knee score, function score and range of motion were improved from 23.1, 35, and 81 to 92.2, 60, and 104.4, respectively. There were no radiological signs of loosening at latest follow-up. The constrained type of knee prosthesis is a good alternative to ligamentous reconstruction in primary TKR with severe varus deformity when ligament imbalance persists after adequate medial soft tissue release. Key Words: Constrained condylar prosthesis; Total knee replacement; Varus




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INTRODUCTION

mary TKR with severe valgus deformity.2-4,7,9,14

The constrained type of knee prosthesis has been used since the mid-1970s. It was mainly used for revision after the early failure of hinged knee prosthesis. Most of the literature supports its use in revision TKR and pri-

Chinese patients with severe varus deformity (>20˚) tend to have their TKRs done in a relatively late stage (Fig. 1). The degree of lateral collateral ligament laxity

Correspondence: Dr. K.H. Chiu, Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, 5/ F, Clinical Sciences Building, Prince of Wales Hospital, Shatin, New Territories, Hong Kong. © 2002 Hong Kong Orthopaedic Association & Hong Kong College of Orthopaedic Surgeons.

65

HKJOS

Cheung KW, Yung SHP, Chiu KH

Figure 2 Lateral collateral ligament imbalance of greater than 2 mm after adequate medial soft tissue release.

Figure 1 Severe preoperative varus deformity of greater than 30˚.

is proportional to the degree of varus deformity preoperatively. Mild to moderate degrees of lateral collateral ligamentous laxity (grades I and II) can be balanced by medial soft tissue release. Grade III lateral collateral ligamentous laxity that cannot be compensated for by a greater extent of medial soft tissue release requires collateral ligamentous reconstruction17 or medial capsular recession.11-13 However, ligamentous reconstruction is time consuming, has relatively less predictable results, and expertise is required for its performance.15 Constrained condylar knee prosthesis has a deepened femoral notch and a relatively higher and broader tibial insert spine, which thus provides medial-lateral stability (allowing 3˚ varus-valgus tilt and 5˚ internal-external rotation). Its use can be extended to primary TKR with severe varus deformity and unbalanced lateral collateral ligamentous laxity; however, the constrained type of knee prosthesis entails the theoretical risk of increased stress transfer to bone, which can lead to early loosening of the prosthesis.

66

We aim to study the clinical and radiological results of CCK prosthesis in primary TKR with severe varus deformity. We would also like to find out whether the degree of preoperative varus deformity can predict the likelihood of using the constrained type of knee prosthesis.

METHODS From 1996 to 1999, thirteen TKRs with CCK prosthesis (Zimmer, Warsaw, Ind, US) were performed. The use of constrained knee prosthesis was determined intraoperatively when medial-lateral ligamentous imbalance was more than 2 mm after adequate medial soft tissue release (Fig. 2). The male to female patient ratio in this study was 1:2 and average age was 65.7 years (range, 37-77 years). There were 12 knees with osteoarthritis and 1 with psoriatic arthropathy. The average preoperative varus deformity was 24.6˚. Knee Society Score8 and the Knee Society Roentographic Evaluation System5 were used to assess the patients’ clinical and radiological results at latest follow-up. The likelihood of using constrained knee prosthesis in varus deformity of the knee was determined by analysing the assessments’ results together with those of 150 posterior stabilised prostheses (Insall-

Primary CCK in severe varus knee

Table 1 Relationship of preoperative varus deformity and the likelihood of using constrained condylar knee prosthesis. Degree of preoperative varus deformity 20˚ 25˚ 30˚ 35˚

CCK Group 7 2 2 2

PS CCK/(CCK+PS) Group % 17 1 0 0

29 67 100 100

CCK = constrained condylar knee; PS = posterior stabilised knee

Burnstein II, Zimmer) that were performed during the same period. The chi-square test was used and the alpha level was set at 0.05.

RESULTS The average follow-up duration in this study was 3.2 years (range, 2-5.4 years). The average knee score improved from 23.1 (range, 0-39) to 92.2 (range, 77-100) at latest follow-up. All patients demonstrated good or excellent results. The average function score of the CCK improved from 38.5 (range, 0-55) to 60 (range, 0-100) at latest follow-up. Fifty-four percent of the CCK group patients demonstrated good or excellent results. The average range of motion improved from 81˚ (range, 10˚90˚) to 104.4˚ (range, 85˚-120˚). There were no complications in the CCK group. There were no radiological signs of loosening at latest followup. The average anteroposterior femoral joint angle (α) and anteroposterior tibial angle (β) were 95.8˚ and 89˚, respectively. In our study, a prediction of the likelihood of using the constrained type of knee prosthesis with a certain degree of preoperative varus deformity was attempted. When the varus deformity was 20˚ or more, the probability of using a constrained prosthesis was 29%. The probability of using a constrained prosthesis was raised to 67% when the varus deformity was 25˚ or more, and it was further raised to 100% when the varus deformity was 30˚ or more (p