Pseudo-patella baja (PPB) describes narrowing of the distance between the patella and the tibia without shortening of the PT and occurs following Total Knee Arthroplasty (TKA), where the tibial prosthesis plus insert are thicker than the resected tibia. Soft tissue balancing is an important factor in the success of TKA, but if extensive may necessitate the use of thicker tibial inserts with the risk of creating a PPB. Patients who undergo extensive soft tissue releases during TKA, with resultant use of thicker tibial inserts will develop a PPB, with increased risk of patella pathology.

506 patients aged 40-90 years underwent 526 Kinemax TKAs, performed by 7 surgeons in 5 centres between 1999 and 2002. The extent of soft tissue releases and the thickness of tibial inserts were recorded. Pre- and post-operative lateral radiographs were measured by an independent observer, using the Caton-Deshamps method to assess patella position. The patients were assessed using the Oxford Knee Score and the American Knee Society Clinical Rating System, with a minimum follow-up of 12 months.

1. TKA surgery creates a Pseudo-Patella Baja. Excluding patients with a pre-operative patella baja, PPB was introduced into 26.7% of patients. (p=0.000). 2. The incidence of pseudo-patella baja increased with the extent of soft tissue release; Minimal, Moderate or Extensive. (p=0.000). 3. The incidence of pseudo-patella-baja increased with increases in insert thickness. Three groups were identified: Inserts 8 mm, inserts 10-12mm, and inserts 15-22 mm. (p=0.035). There was no correlation between the incidence of PPB and changes in clinical or functional outcome, as measured using the OKS and AKSS.

Pseudo-patella baja occurs in 26% of all patients following TKA, and in 46% of patients in whom extensive soft tissue releases have been performed and/or large tibial inserts have been used. At 12 months, no detrimental outcomes were attributable to the incidence of pseudo-patella baja.

Introduction: Patella baja is the distal positioning of the patella in relation to the femoral condyles in the sagittal plane. True patella baja is due to shortening of the patella tendon (PT), as measured by the Insall-Salvati method, and narrowing of the distance between the patella and the proximal tibia. Pseudo-patella baja describes narrowing of the distance between the patella and the proximal tibia without shortening of the PT and occurs following Total Knee Arthroplasty (TKA), where the tibial prosthesis plus insert are thicker than the resected tibia. Both may cause patella pathology, pain and a reduced range of motion. Pseudo-patella baja can be detected using the Caton-Deschamps method.

Soft tissue balancing is an important factor in the success outcome of TKA, but if extensive can necessitate the use of thicker tibial inserts. This may alter the position of the patella in relation to the tibia and increases the risk of creating a pseudo-patella baja.

Hypothesis: Patients who undergo extensive soft tissue releases during TKA, with the resultant use of thicker tibial inserts will develop a pseudo-patella baja, and will have a poorer outcome and reduced range of motion.

Method: In this prospective study, 506 patients aged 40–90 years underwent 526 Kinemax TKAs, performed by 7 surgeons in 5 centers between October 1999 and December 2002. The extent of soft tissue releases and the size of tibial inserts were recorded. Independent observers used the Caton-Deshamps method to assess patella position measured Pre and post-operative lateral radiographs. The patients were also assessed using the Oxford Knee Score and the American Knee Society Clinical Rating System, with a minimum follow-up of 12 months.

Results:

TKA surgery creates a Pseudo-Patella Baja. Excluding patients with a pre-operative patella baja, pseudo patella baja was introduced into 25.6% of patients. (p=0.00).

Conclusion: Pseudo patella baja occurs in 25% of all patients following TKA, and in over 40% of patients in whom extensive soft tissue releases have been performed and/or large tibial inserts have been used. At 12 months, no detrimental outcomes were attributable to the incidence of pseudo patella baja.

Introduction: Soft tissue balancing is an important factor in the success of TKA, but if extensive may necessitate the use of thicker tibial inserts with the risk of creating a Pseudo-patella baja (PPB), which describes narrowing between the patella and the tibia without shortening of the PT, and occurs when the tibial prosthesis plus insert are thicker than the resected tibia.

Hypothesis: Patients who undergo extensive soft tissue releases during TKA, with resultant use of thicker tibial inserts will develop a PPB, with increased risk of patella pathology.

Method: 506 patients aged 40–90 years underwent 526 Kinemax TKAs, between 1999 and 2002. The extent of soft tissue releases and thickness of tibial inserts were recorded. Patella height was measured on pre and postoperative radiographs by an independent observer. Outcome was assessed using the Oxford Knee Score and the American Knee Society Clinical Rating System, with a minimum follow-up of 12 months.

Results:

TKA surgery creates a Pseudo-Patella Baja. PPB was introduced into 26.7% of patients. (p=0.000).

There was no correlation between the incidence of PPB and changes in outcome, as measured using the OKS and AKSS.

Conclusion: Pseudo patella baja occurs in 26% of all patients following TKA, and in 46% of patients in whom extensive soft tissue releases have been performed and/or large tibial inserts have been used. AT 12 months, no detrimental outcomes were attributable to the incidence of pseudo patella baja.

Soft tissue balance is known to be an important factor for the success of Total Knee Arthroplasty.Traditional surgical techniques involve soft tissue releases and bony cuts to achieve the correct balance. Evaluation of balance is currently based on subjective intra-operative clinical assessment, or the feel of the knee. More recently, an instrument to objectively measure soft tissue balance following bony cuts has been developed. Soft tissues releases using this instrument may be extensive.

Hypothesis. The hypothesis is that patients who undergo more extensive releases will have poorer short-term outcome and increased complication rates compared to those who undergo less extensive releases.

Method. 506 patients aged 40–90 years underwent 526 Kinemax TKAs, performed by seven surgeons in five centres between October 1999 and December 2002. Five surgeons used traditional methods for soft tissue balancing and only took balancer measurements pre-cementation. The other two were guided by the balancer instrument and took measurements pre- and post-releases, therefore quantifying how imbalanced the knees were at the beginning of the operation. Patients were assessed by an independent observer using the Oxford Knee Score, the American Knee Society Clinical Rating System and the Roentographic and Evaluation Scoring System, with a minimum follow-up of 12 months.

Results. Extensive soft tissue releasing procedures showed no significant difference in outcome in comparison with minimal releases. For the 2 surgeons using the balancer technique, a significant difference was seen with the change in knee scores. The knees left imbal-anced had substantially lower change scores and the imbalanced – balanced group showed the most improvement. Regarding surgical technique, there was no significant difference between the groups with the Oxford Knee Score or with the Clinical Rating System. Range of movement and outcome also showed no significant difference between any of the groups. Complication rates were low, clinically representative and showed no significant difference between the groups.

Conclusions. Extensive soft tissue releases do not result in an increase in complication rate or a poorer short-term outcome. When comparing traditional and balancer guided techniques there is no difference in outcomes. Balancing an imbalanced knee significantly improves knee outcome.