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.

Flexion contracture in total knee arthroplasty (TKA) remains a challenge. Soft tissue management and additional bone resection are traditional options for flexion contracture correction. Our hypothesis was that the post implant computer aided measurements would not be significantly different to the extension angles measured at six weeks post-operatively in the follow-up clinic.

One hundred continuous TKA were performed by a single consultant using the OrthoPilot^® (BBraun, Aesculap) navigation system and Columbus implants. Of the group, 45 were male and 55 were female. Average age was 68 (range 49–87), mean BMI was 32.86 (22.26–51.86) and mean Oxford score preoperatively was 42 (range 21–56) and post-operatively 28 (range15–50). Data recorded at the preoperative assessment clinic included clinical flexion contracture and Oxford scores. Intra-operatively data were recorded using the navigation system. These included pre-operative flexion and extension angles, actual bone cuts of tibia and femur (both medial and lateral), postoperative correction of flexion and extension angles and soft tissue releases. At six weeks post operation, patients were seen in the follow clinic and clinical flexion contracture and Oxford score reassessed by the Arthroplasty outcome service.

Measurements were grouped and comparisons were made using a Pearson Chi-square test. There was no relationship between post-implant extension angle measurements (by computer) and extension angles at six weeks (by goniometer) (p=0.682). Also, there was no relationship between pre-operative measurement angles collected at the pre-assessment (by goniometer) and the pre-implant angles measured on the table (by computer) (p=0.682). We found that BMI (up to 35) and postoperative Oxford scores were significantly related to the extension levels with values of (p=0.008) and (p=0.027) respectively. Pre-operative Oxford scores, pre-operative extension, amount of bony resection and soft-tissue releases did not show any significant relationship with the post-operative extension obtained at six weeks.

The conclusions that we draw from this study are that there might be other factors that are likely to influence extension lag between the operation and the follow-up at six weeks. One of the factors that we could identify was the BMI. Attention to extensor lag is important because it leads to a poorer knee function, as indicated by the Oxford scores. Despite most of the post-implant measurement angles showing no extensor lag, about 20% of our patients still had more than five degrees flexion contracture at six weeks.

Flexion contracture is a common deformity encountered in patients requiring total knee arthroplasty (TKA). 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 TKA 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.

One hundred and four continuous TKA were completed by a single consultant using the OrthoPilot® (BBraun, Aesculap) navigation system and Columbus implants. Seventy-four 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 (four 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 TKA 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 TKA 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.