Abstract
INTRODUCTION
Soft tissue balancing in knee arthroplasty remains an art. To make it a science reliable quantification and reference values for soft tissue tension and contact loads are necessary. This study intends to prove the concept of a compartmental load safe target zone as a clinical tool for balancing total knee arthroplasties by studying the relationship between post- balancing compartmental load distribution and patient satisfaction at 6 months.
MATERIALS AND METHODS
In this prospective non-randomised clinical series of 102 patients (110 knees), medial and lateral loads were recorded intra-operatively using a tibial liner load sensor system. All knees were balanced using specific algorithm sequences with a goal of equal distribution between compartments. A safe target zone area was defined on a scatterplot graph displaying lateral versus medial loads. Individual points on the graft were coded with their satisfaction score at 6 months.
RESULTS
Eighty-two (82) cases satisfied the study criteria and were analysed. The boundaries of the safe zone were defined by combining absolute and relative load values. Fifty-seven (57) knees fitted in the defined zone and 25 lied outside. Excellent satisfaction scores were 4.2 times more likely to be in the safe zone. Poor scores were twice more likely to lie outside the zone. In the zone the median satisfaction score was 36/40, whereas outside the zone it fell to 31/40.
DISCUSSION
Load balancing of knee arthroplasty is a useful clinical tool. Early studies by a developing group showed increased satisfaction rates. One problem remains the subjectivity of testing at the time of surgery. Other studies have also pointed to the difficulty in defining a target zone for balancing. Using specific ligamentous balance algorithms it is now possible to predictably achieve a balanced load differential within 15 lbs between compartments. In this paper, we have demonstrated in a prospective series that a target zone can be defined as an area rather than a single ideal value. Within this zone satisfaction scores reach 90–95%. Of all excellent results there are 4.2 more within the zone than outside. Balancing a knee arthroplasty to medial and lateral compartment load values defined by a safe target zone can therefore be predictive of patient satisfaction.
