Principles of the 'SAIPH® Medially Stabilised' Knee
- Products
- SAIPH® Knee System
- Principles of SAIPH®
Tibiofemoral Articulation
The SAIPH® Knee design is based on the principle of medial stability in the normal knee, which has been described in historical literature2 and widely in recent literature3,4,5.
In normal, healthy knees the shapes of the medial and lateral tibial condyles are different: the medial side is concave; the lateral side is convex. Stability is provided collectively by the collateral ligaments (MCL and LCL), both cruciate ligaments (ACL and PCL) and the menisci.
The shapes of the articular surfaces and the arrangement of stabilising soft tissue structures collectively provide greater stability about the medial condyle. Knee flexion is accompanied by axial rotation of the femur with respect to the tibia, which is achieved with a limited freedom for antero-posterior (AP) movement of the lateral femoral condyle relative to the tibia.
Stability throughout flexion is crucial to normal knee function: a knee with a deficient ACL or medial meniscus, for example, is likely to be unstable and may require corrective surgery. Standard TKRs require removal of the menisci, ACL and commonly the PCL, and they do not fully substitute for their functions. Those that intend to retain the PCL may not reliably do so6.
The SAIPH® Knee is different: it substitutes for all the removed structures. Inherent stability is provided throughout the full range of motion (ROM) with a medial deep-dish ball-and-socket articulation7. A semi conforming lateral articulation permits AP translation during activities that require it while limiting excessive (unnatural) movement7.
This clinical rationale describes the clinical evidence that the SAIPH® Knee provides inherent stability, a near normal tibiofemoral kinematic pattern and no restriction to the patient’s range of motion. It also describes data that links these features to a demonstrably higher rate of patient satisfaction.
Patellofemoral Articulation
Whether or not the patella is resurfaced, TKR surgery includes replacing the patellofemoral articulation. Hence, the patellofemoral joint (PFJ) design is equally important for any high-functioning TKR device. The normal trochlea is lateral to the midline8,9 and with an asymmetric patella the normal patella tracks laterally in flexion9,10. The lateralised patella also plays a role in stabilising the lateral tibiofemoral articulation.
Most standard TKR devices are restricted to a centrally located trochlea – a necessity for standard femoral condylar design11 – and the resulting patella tracking does not compare well to the normal knee12. The SAIPH® Knee, however, features a physiologically lateralised trochlea, like the MRK11,12, which exhibits a similar amount of lateral patella translation during flexion as patients without a TKR12.
With the right trochlea design, choosing not to replace the patella has not been shown to influence outcomes13. Nevertheless, the SAIPH® Knee is available with the same unique saddle-shaped patella, which can rotate to match the femur for a fully conforming interface, and has 40 years of successful clinical heritage13,14,15,16,17. The SAIPH® Knee is also available with a cemented dome-shaped patella button.
References
- MatOrtho® data, 1 May 2022.
- Pinskerova V, Maquet P, Freeman MAR. Writings on the knee between 1836 and 1917. J Bone Joint Surg Br. 2000; 82(8):
1100-1102. - Iwaki H, Pinskerova V, Freeman MA. Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee. J Bone Joint Surg Br. 2000; 82(8):1189-95.
- Hill PF, Vedi V, Williams A, Iwaki H, Pinskerova V, Freeman MA. Tibiofemoral movement 2: the loaded and unloaded living knee studied by MRI. J Bone Joint Surg Br. 2000; 82(8):1196-8.
- Johal P, Williams A, Wragg P, Hunt D, Gedroyc W. Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using ‘interventional’ MRI. J Biomech. 2005; 38(2):269-76.
- Shannon FJ, Cronin JJ, Cleary MS, Eustace SJ, Byrne JMO. The posterior cruciate ligament-preserving total kneereplacement: do we ‘preserve’ it? A radiological study. JBJS(Br). 2007; 89-B:766-771.
- Shimmin A, Martinez Martos S, Owens J, Iorgulescu AD, Banks S. Fluoroscopic motion study confirming the stability of a medial pivot design total knee arthroplasty. The Knee. 2015; 22(6): 522-526.
- Eckhoff DG, Montgomery WK, Stamm ER and Kilcoyne RF. Location of the Femoral Sulcus in the Osteoarthritic Knee. J of Arthrop. 1996; 11 (2): 163-165.
- Iranpour F, Merican AM, Dandachli W, Amis AA, Cobb JP. The geometry of the trochlear groove. Clin Orthop Relat Res. 2010; 468(3):782-8.
- Katchburian MV, Bull AM, Shih YF, Heatley FW, Amis AA. Measurement of patellar tracking: assessment and analysis of the literature. Clin Orthop Relate Res. 2003; 412: 241-59.
- Schindler OS. The controversy of patellar resurfacing in total knee arthroplasty: Ibisne in medio tutissimus? Knee Surg Sports Traumatol Arthrosc. 2012; 20:1227-1244 (ref. Figure 8, p1233).
- Rhee SJ, Hossain F, Konan S, Ashby E and Haddad F. Patellar Tracking: A Comparison of an Implant with a Lateralised Trochlear Groove Compared to a Conventional Posterior Stabilised Design. J Bone Joint Surg Br 2012; 94-B no. SUPP IX 90.
- Kulkarni SK, Freeman MA, Poal-Manresa JC, Asencio JI, Rodriguez JJ. The patellofemoral joint in total knee arthroplasty: is the design of the trochlea the critical factor? J Arthroplasty. 2000; 15(4):424-9.
- Amin A, Al-Taiar A, Sanghrajka AP, Kang N, Scott G. The early radiological follow-up of a medial rotational design of total knee arthroplasty. Knee 2008; 15(3):222-6.
- Mannan K and Scott G. The Medial Rotation total knee replacement: a clinical and radiological review at a mean followup of six years. J Bone Joint Surg Br. 2009; 91(6):750-6.
- National Joint Registry. Implant Summary Report for the MRK. Summary.Report.KP_Femoral_MRK.18/02/2022.
- National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. 18th Annual Report, 2021: Surgical data to 31 December 2020. www.njrreports.org.uk.
Resources
SAIPH® Clinical Rationale
SAIPH® Flyer
SAIPH® Operative Technique
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Clinical Heritage: Success of the MRK™
The MRK™, also manufactured by MatOrtho® (previously Finsbury), is the original 1994 ‘medial ball-and-socket knee’ and remains in popular use. The clinical success of the MRK™ has strong relevance as a ‘proof of concept’ to the expected long-term outcomes for the SAIPH® Knee, which is an evolution of the original design.