Insall et al. report the first 2-4 year clinical outcomes of the Posterior Stabilized (PS) condylar prosthesis, introduced in 1978 as a modification of the Total Condylar design. The PS implant replaces PCL function with a tibial polyethylene spine and transverse femoral cam. Results in 118 arthroplasties are compared against historical Total Condylar controls using identical HSS scoring methodology.
The Total Condylar prosthesis was already successful, but fewer than one-quarter of patients could climb stairs normally, and average ROM was only 90°. Those limitations drove Insall to redesign the implant around controlled femoral rollback.
This paper is why PS TKA became the default choice for knees with severe deformity, PCL deficiency, or cases where maximizing flexion and functional stair-climbing matters most. When you see a patient with a flexion contracture greater than 10-15° or significant coronal plane deformity requiring extensive ligament release, the PS design's cam provides a reliable stability backstop that the Total Condylar design cannot.
On the patella: the intercondylar box geometry and greater ROM both increase patellar loading. Use the smallest patellar button that provides adequate coverage, verify central tracking before closure (the patella should track without thumb pressure), and perform lateral release or proximal realignment proactively rather than reactively.
This paper directly launched the Insall-Burstein PS knee system and established the cam-spine mechanism as the defining feature of the PS design class still in use today.
Insall et al. report the first 2-4 year clinical outcomes of the Posterior Stabilized (PS) condylar prosthesis, introduced in 1978 as a modification of the Total Condylar design. The PS implant replaces PCL function with a tibial polyethylene spine and transverse femoral cam. Results in 118 arthroplasties are compared against historical Total Condylar controls using identical HSS scoring methodology.
The Total Condylar prosthesis was already successful, but fewer than one-quarter of patients could climb stairs normally, and average ROM was only 90°. Those limitations drove Insall to redesign the implant around controlled femoral rollback.
This paper is why PS TKA became the default choice for knees with severe deformity, PCL deficiency, or cases where maximizing flexion and functional stair-climbing matters most. When you see a patient with a flexion contracture greater than 10-15° or significant coronal plane deformity requiring extensive ligament release, the PS design's cam provides a reliable stability backstop that the Total Condylar design cannot.
On the patella: the intercondylar box geometry and greater ROM both increase patellar loading. Use the smallest patellar button that provides adequate coverage, verify central tracking before closure (the patella should track without thumb pressure), and perform lateral release or proximal realignment proactively rather than reactively.
This paper directly launched the Insall-Burstein PS knee system and established the cam-spine mechanism as the defining feature of the PS design class still in use today.