Increased knee flexion is seen as a primary goal in achieving a better functional outcome following TKR. However, the relationship between passive knee flexion and biomechanical outcome remains unclear. The aim of this study was to compare kinematic outcomes in TKR patients and controls during high flexion activities.

A three dimensional motion analysis system and two force platforms were used to collect kinematic and kinetic data from 40 patients who had undergone total knee replacement at least 12 months previously and 40 controls who were matched to the patients for age and gender. Participants completed the following activities six times: standing from a seated position, squatting, and lunging with each leg leading. Peak knee flexion angles and moments were compared between groups using t-tests and the correlations between passive knee flexion and functional knee flexion were calculated using ‘Pearson's r’.

For both squatting and lunging, peak knee flexion in the TKR group was significantly less than in the control group. There was no difference between the two groups for the sit to stand activity as peak flexion for this activity was primarily determined by the chair height.

Squat: control 124, TKR 91 (p<0.001) Lunge - op. forward: control 100, TKR 81 (p<0.001) Lunge - op. trail: control 106, TKR 84 (p<0.001) Sit to stand: control 87, TKR 85 (p=0.5)

Although there were significant correlations between functional and passive knee flexion in the TKR group for the squatting and lunging activities, the patients used only approximately 70 to 75% of their available flexion during these activities. As anticipated, there was only a weak correlation between passive and functional flexion for the sit to stand activity.

Percentage of passive flexion used: squat: 77%, lunge - op. forward: 68%, lunge - op. trail: 70% Sit to stand: 71%, Correlations: squat: 0.50, lunge - op. forward: 0.57, lunge - op. trail: 0.50, Sit to stand: 0.27

Normal sagittal knee kinematics during high flexion activities was not restored following TKR. Patients did not or were unable to use their available range of flexion to achieve a normal kinematic pattern. The cause of this important functional deficit remains to be established but may be amenable to targeted rehabilitation.

High tibial osteotomy (HTO) is an established treatment for medial compartment osteoarthritis of the knee; the aim being to achieve a somewhat valgus coronal alignment, thereby unloading the affected medial compartment. This study investigated knee kinematics and kinetics before and after HTO and compared them with matched control data.

A three dimensional motion analysis system and two force platforms were used to collect kinematic and kinetic data from eight patients with medial compartment knee osteoarthritis during walking preoperatively and 12 months following HTO (opening wedge). Nine control participants of similar age and the same sex were tested using the same protocol. Sagittal and coronal knee angles and moments were measured on both the operated and non-operated knees and compared between the two time points and between HTO participants and controls. In addition, preoperative and postoperative radiographic coronal plane alignments were compared in the HTO participants.

The point at which the mechanical axis passed through the knee joint was corrected from a preoperative mean of 10% tibial width from the medial tibial margin to 56% postoperatively. Stride length and walking speed both improved to essentially normal levels (1.57 m and 1.5 m/s) ostoperatively. In the coronal plane the mean peak adduction angle during stance reduced from 14.3° to 5.2° (control: 6.8°). Mean maximum adduction moments were similarly reduced to levels less than in control participants, in keeping with the aim of the surgical procedure: peak adduction moment 1: pre 3.8, post 2.7, control 3.6 peak adduction moment 2: pre 2.5, post 1.7 and control 2.6.

In the sagittal plane, both mean maximum flexion and extension during stance increased postoperatively—extension to greater than in control participants and flexion to almost control levels. The maximum external knee flexor moment during stance also increased to near normal postoperatively.

High tibial osteotomy appears to achieve the intended biomechanical effects in the coronal plane (reduced loading of the medial compartment during stance). At the same time there were improvements in sagittal plane kinematics and kinetics which may reflect a reduction in pain. The net effect was to reduce quadriceps demand.