FLEXION CONTRACTURE IN TOTAL KNEE REPLACEMENT: THE INFLUENCE OF BONE CUTS

Abstract

Flexion contracture is a common deformity encountered in patients requiring total knee replacements (TKR). Both the soft tissue envelope and articular bones are involved in the knee extension lag. A few studies in the past have assessed the relationship between bone cuts and extension deficit by using goniometers and rulers. Using navigation for TKR enables the accurate measurement of knee flexion contracture and bone cuts. The aim of this study was to try to establish a relationship between extension lag correction and the size of bone cuts made.

104 continuous TKR were completed by a single consultant using the OrthoPilot^® (BBraun, Aesculap) navigation system and Columbus implants. 74 knees had preoperative flexion contracture (including neutral knees) while 30 were in hyperextension. Data was recorded prospectively using the navigation system. These included preoperative flexion and extension angles, actual bone cuts of tibia and femur (both medial and lateral), postoperative correction of flexion and extension angle, size of the prosthesis with thickness of polyethylene and soft tissue release. Of the 74 knees with fixed flexion, 57 had no release and 13 had a posterior release (4 had an intermediate release and were excluded from the study).

For knees with fixed flexion (n=70) there was a significant statistical difference between the pre and post implant extension angle (p < < 0.0001). There was no correlation between the thickness of bone cuts and postoperative extension lag either for the group with no release (p=0.495) or posterior release (p=0.516). There was also no correlation between bone cuts and preoperative angles for either type of release (p=0.348 and p=0.262). There was a significant difference between the preoperative extension deformity for the two soft tissue releases performed (p=0.00019), the mean fixed flexion angles being −4.4° and −10.4° for no release and posterior release respectively.

Flexion contracture deformity in TKR can theoretically be solved in two ways: either by extensively releasing the soft tissue or by increasing the extension gap by cutting more bone (logically the distal femur). Appropriate soft tissue management and release in TKR is crucial in balancing the prosthesis in the coronal as well as the lateral plane. This study seems to confirm the supremacy of soft tissue management and release over bone cut resection. Cutting more or less bone could in fact lead to a poorer outcome as this will change the joint line level without having any additional beneficial effect in correcting the flexion contracture. Conversely adequate soft tissue release has corrected the flexion contracture when needed. In conclusion, there was no correlation between bone cut resection and extension lag correction and with large extension deficits, a posterior soft tissue release and osteophytes resection was more important than bone cuts.