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Medially Stabilised Knees in the Literature, Part 2 – Technique

Medially Stabilised Knees in the Literature, Part 2 – Technique

Medially stabilised knees stand out in the literature for patient satisfaction and feeling of normality, but some do better than others in functional measures and survivorship. So-called medially stabilised knees are not all the same and this series of articles reviews key differences observed in the literature.


This year’s Forever Active Forum featured a review of the literature on medially stabilised knees by David Wood1. In a short series of articles we expand on the session to discuss factors that can make a difference, including fixation, technique, stability, and the all-important third compartment.

Part 2 – Technique

Application of an appropriate surgical technique is essential for successful TKR. Techniques differ between design concepts and for cruciate-retaining versus cruciate-sacrificing techniques, particular considerations apply to resection and ligament tensioning to avoid flexion instability1,2,3.

Concept for a stabilising bearing design

The original condylar knee concept developed by Freeman and Swanson was designed to give “a determinate axis of flexion-extension, [while] resistance to torsion, abduction, adduction or hyperextension is provided by the collateral ligaments in conjunction with the shape of the prosthetic components4. All subsequent designs in the FS knee series were cruciate sacrificing knees. The implant design and well-considered surgical technique were intended to restore cruciate function. The surgical principles for the MRK™ and SAIPH® are largely unchanged from those of the FS Knee series.

Complete removal of both cruciate ligaments is important for the following reasons:

  • avoids kinematic conflict with the stabilising, cruciate substituting bearing
  • stability requires ACL and PCL or substitution of both (CR and PS knees resect but do not substitute the ACL)
  • a retained PCL is often likely to be incompetent5
  • any residue of intercondylar tissues are likely to limit flexion
  • a cruciate sacrificing approach provides a reliable and repeatable technique for the surgeon (mid-operative conversion not required)

Results impacted by technique

The Advance Medial Pivot (MP) Knee resulted from licensing of the ball-and-socket concept from Finsbury in the 1990s and did not specify complete removal of the PCL. Literature reviews finding an inconsistent outcome for the concept are dominated by studies using this design, some with and some without PCL retention6. One often cited example is a bilateral comparative study of 195 patients (390 knees) using the Advance MP and PFC-Σ CR Knees7. Although the authors note that the MP knees were PCL sacrificing, their earlier report on the first 98 patients explained that the surgical approach was to retain the PCL unless a knee was later found to be stiff8.

Although the authors had cited a study that found similar outcomes for the MP knee whether or not the PCL is retained7,8, that study described regular practice of a single technique by individual surgeons each having clear intent to resect the PCL, or to retain it using a modified technique9. This is not the same as a single surgeon performing MP and CR procedures sequentially under single anaesthetic, retaining the PCL in the MP knees using the standard technique and with frequent subsequent PCL resection after trial assessment8. The compromised range of motion (ROM), recurrent effusions, infections and inevitable dissatisfaction found by the bilateral study authors were caused by inappropriate technique.

Conversely, in a similar comparative study including bilateral procedures using the same MP device and another comparator CR knee, a surgeon had staged all bilateral procedures and modified his technique according to each device’s design features, including complete excision of the PCL in all MP knees. This study found that MP patients were attributed with higher range of motion and higher functional scores than the comparator CR knee10. In terms of the patient’s perspective, 76% of patients preferred the MP design over CR design (12% could not tell; 12% favoured CR knee)10. Furthermore, the MP knees were reported with better ROM and scores than the comparative ACL and PCL retaining device and were as likely to prefer the MP design as the PCL and ACL retaining design! This demonstrates that the medially stabilised concept adequately restores cruciate function as the concept innovators had intended.

Consistent results: medially stabilised knees are better

The medial ball-and-socket principle is a cruciate substituting design: proper implementation of the concept substitutes for the ACL and PCL. Modification of the prescribed technique is hazardous as has been shown for an alternative design and has led to compromised results.

The MRK™ and SAIPH® knees, developed by the concept originators and used with their well-defined technique, have provided the following benefits: negligible risk of dislocation, equivalent preservation of bone stock to a CR knee, maintenance of optimum posterior offset for stable full-range flexion, no risk of post wear (no post), and no risk of instability resulting from subsequent PCL failure.

As a result, the MRK™ and SAIPH® Knees have consistently been shown to deliver superior stability1113 with excellent ROM1215, high functional scores1418 and high levels of satisfaction1418.

By fully substituting for the ACL and PCL, the MRK™ and SAIPH® are well-suited to simple and complex requirements, including knees contraindicated for cruciate-retaining TKR.

  1. D’Anchise R et al. Posterior cruciate ligament-retaining and posterior-stabilized total knee arthroplasty: differences in surgical technique. Joints. 2013; 1(1): 5-9.
  2. Stiehl JB. Principles of Ligament Balancing in Total Knee Replacement. J Traum & Orthop. ; 2(1): 63-67
  3. Babazadeh S et al. The relevance of ligament balancing in total knee arthroplasty: how important is it? A systematic review of the literature. Orthop Reviews. 2009; 1: e26.
  4. Freeman et al. Total Replacement of the Knee Using the Freeman-Swanson Knee Prosthesis. 1973. Clin Orthop & Rel Res. 2003; 416: 4-21.
  5. Shannon et al. The posterior cruciate ligament-preserving total knee replacement: do we ‘preserve’ it? A radiological study. J Bone Joint Surg. 2007; 89-B: 766-771.
  6. Young et al. A Systematic Review of Clinical Functional Outcomes After Medial Stabilized Versus Non-Medial Stabilized Total Knee Joint Replacement. Front. Surg. 2018; 5 Article 25: 1-16.
  7. Kim YH et al. Clinical Outcome of Medial Pivot Compared With Press-Fit Condylar Sigma Cruciate-Retaining Mobile-Bearing Total Knee Arthroplasty. J Arth. 2017; 32(10): 3016-3023.
  8. Kim YH et al. Early outcome of TKA with a medial pivot fixed-bearing prosthesis is worse than with a PFC mobile-bearing prosthesis. Clin Orthop Rel Res. 2009; 467(2): 493-503.
  9. Bae DK et al. Clinical Outcome of Total Knee Arthroplasty with Medial Pivot Prosthesis. A Comparative Study between the Cruciate Retaining and Sacrificing. J Arth. 2011; 26(5): 693-698.
  10. Pritchett J. Patients prefer a bicruciate-retaining or the medial pivot total knee prosthesis. J. Arth. 2011; 26(2): 224-228.
  11. Shah S et al. The Influence of Implant Design on Sagittal Stability of Total Knee Replacement. Presented at the AOA ASM, Brisbane, 2015.
  12. Moonot P et al. Tibiofemoral kinematic analysis of knee flexion for a medial pivot knee. Knee Surg Sports Traumatol Arthrosc. 2009; 17: 927–934
  13. 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. Knee. 2015; 22(6): 522-526.
  14. Walter et al. SAIPH® Medial Ball and Socket Knee: 2-year Follow-Up of the First 200 Patients. Presented at the AOA ASM, Brisbane, 2016.
  15. Katchky A et al. Minumum 5-year Follow-Up of the SAIPH® Medial Ball and Socket TKR. Presented at the AOA ASM, Adelaide, 2017.
  16. Baré J et al. Results of a Multicentre Study. Presented at the Forever Active Forum, Melbourne, 2018.
  17. Hossain F et al. Knee Arthroplasty With a Medially Conforming Ball-and-Socket Tibiofemoral Articulation Provides Better Function. Clin Orthop Rel Res. 2011; 469: 55-63.
  18. Brighton R. Cruciate Retaining Knee vs. Medial Pivot: Is there a difference in PROMs? Presented at the Forever Active Forum, Melbourne, 2018.