Zimmer Modular Neck Technology

Restoring leg length, joint stability, and range of motion involve distinct surgical challenges. The Zimmer M/L Taper Hip Prosthesis with Kinectiv Technology introduces a system of modular stem and neck components designed to help the surgeon restore the hip joint center intraoperatively by addressing leg length, offset, and version independently. The resulting array of neck options efficiently targets a broad range of male and female patient anatomies.

  • Independent leg-length and offset adjustability to optimize hip joint kinematics and function
  • Independent version adjustability to optimize head center position without affecting proximal stem fit, leg length, or offset
  • Reduced neck geometry and anteverted/retroverted neck options for efficient impingement resolution and enhanced range of motion, which helps to mitigate the risks of accelerated implant wear and dislocation
  • Broad range of head centers better match the wide range of patient anatomies among men and women, help avoid low, bone-sacrificing neck cuts, and provide more opportunities to optimally restore fit and function in the limited-view environment encountered in minimally invasive hip procedures
  • Low-profile implant eases stem insertion and minimizes soft-tissue trauma

Independent Control

Proper offset and leg-length restoration improve total hip replacement function and minimize the risk of dislocation and limp.1,2 For traditional hip systems, leg length and offset are coupled and surgeons are often forced to accept the coincidental change in leg length or offset when making changes intraoperatively (ie, when simply changing the head). The Zimmer M/L Taper Hip Prosthesis with Kinectiv Technology allows surgeons to independently adjust leg length and offset intraoperatively after stem implantation to optimize each dimensional factor without affecting the other.

The Zimmer M/L Taper Hip with Kinectiv Technology also allows independent version adjustments after stem implantation. This facilitates optimal stem position based on the patient’s proximal femoral anatomy while restoring head center position.

Proper offset and leg-length restoration improve total hip replacement function and minimize the risk of dislocation and limp.1,2 For traditional hip systems, leg length and offset are coupled and surgeons are often forced to accept the coincidental change in leg length or offset when making changes intraoperatively (ie, when simply changing the head). The Zimmer M/L Taper Hip Prosthesis with Kinectiv Technology allows surgeons to independently adjust leg length and offset intraoperatively after stem implantation to optimize each dimensional factor without affecting the other.

The Zimmer M/L Taper Hip with Kinectiv Technology also allows independent version adjustments after stem implantation. This facilitates optimal stem position based on the patient’s proximal femoral anatomy while restoring head center position.

Independence

  • Independent leg-length and offset adjustability following stem implantation
  • Leg-length discrepancy is a leading source of patient dissatisfaction in total hip replacement3-6

Version By Design

  • Independent version adjustability following stem implantation
  • Progressively increasing version with decreasing offset to better match patient anatomy
  • Intraoperative range of motion adjustment to resolve impingement and mitigate risk of accelerated implant wear and dislocation

Intraoperative Flexibility

  • No need for surgeon to adjust stem fit to achieve version
  • Version options to optimize stem fit and head center location

Range Of Motion

Impingement of the femoral and acetabular components has been shown to increase risk of dislocation and accelerate wear of the liner.8,9 Since Kinectiv Technology uses +0 heads only, the geometry of each neck component can be specifically optimized for strength and range of motion based on the +0 head length. Kinectiv Technology also eliminates the use of skirted femoral heads that are necessary for the longer offset options of other designs. In addition, the ante/retroverted necks allow the surgeon to adjust version intraoperatively after cup and stem implantation and further fine-tune the range of motion for the patient.

Anteverted And Retroverted Necks

  • When cup placement is not optimal, version options can relieve impingement
  • Version options provide opportunity for surgeon to intraoperatively tune the range of motion to avoid dislocation
  • Dislocation is the second most prevalent complication in total hip replacement, with a 2%-4% incidence10-12
  • Dislocation is a significant financial burden to the healthcare system13

Technology

Years of extensive engineering design, laboratory testing, and clinical consultation have been devoted to optimize the structural integrity, wear debris characteristics, and clinical presentation of the implants and instruments.

Strength

The neck and stem components of the Zimmer® M/L Taper Hip Prosthesis with Kinectiv® Modular Neck Technology have passed extensive laboratory fatigue testing, enduring the same stringent requirements as other Zimmer primary hip stems, such as the clinically successful Zimmer M/L Taper Hip Prosthesis and VerSys ® Hip System implants. The strength requirements led to the deliberate design of the proximal stem geometry as well as the amount of version provided by the neck components. The implants for performance fatigue testing were carefully selected via bench testing and exhaustive finite element analysis to ensure that the worst-case combinations of components were tested in anteverted, straight, and retroverted configurations.

Modular Junction Stability

Using long-term clinical retrieval feedback of modular junctions that have been used successfully for many years, Zimmer developed a challenging test to replicate the most aggressive clinical fretting corrosion response. This accelerated corrosion fatigue test development considered test factors including load magnitude, test frequency, number of cycles, solution pH, and solution temperature. Further advances in the test technique allowed for quantification of mass loss from the head, neck, and stem components. Internal mass–loss testing has shown that the combined wear debris of the titanium-titanium Kinectiv Technology junction using an extra-extended offset neck with a +0 cobalt chrome femoral head is less than that of a +10.5 cobalt chrome femoral head on traditional titanium femoral hip stems.1 The use of +0 heads provides a significant advantage in regard to wear debris that can result in amounts less than that produced by traditional stem-head constructs.

Due to the nature of the Kinectiv Technology neck modularity, it is necessary to have a secure lock and fit of the components such that they do not disassemble in vivo. Neck distraction testing was conducted to evaluate the security following simulated mild assembly of the components. The force required to distract the neck components from the stem was greater than that required to distract femoral heads from traditional stem tapers.

Simplicity

With the modular neck there are many more options, but there is also the risk of increased complexity. Kinectiv Technology implants and instrumentation have been designed with significant consultation with surgeons, OR personnel, and sales representatives. The keystone for simplicity is the use of +0 heads only. This eliminates the need for multiple head lengths, complicated charts, and head-size limitations and allows truly independent leg-length and offset adjustment. The intuitive and readily apparent leg-length and offset adjustments improve operative flow. The neck provisional layout within the provisional tray mimics the template of head centers so that one simply needs to select the neck provisional that matches the template head center location.

References

  1. Data on file at Zimmer.
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References

  1. Iorio R, Healy W,L Warren PD, Appleby D. Lateral trochanteric pain following primary total hip arthroplasty, J Arthroplasty 2006;21:233-236.
  2. Bourne RB and Rorabeck CH. Soft tissue balancing the hip. J Arthroplasty. 2002;17(Suppl 1):17-22.
  3. Konveys A and Bannister GC. The importance of leg length discrepancy after total hip arthroplasty. J Bone Joint Surg Br. 2005;87-B:155-157.
  4. Hoffmann AA and Skrzynski MC. Leg length inequality and nerve palsy in total hip arthroplasty: A lawyer awaits! Orthopaedics 2000;9:943-944.
  5. White AB. AAOS Committee on professional liability: Study of 119 closed malpractice claims involving hip replacement. AAOS Bulletin July 1994.
  6. Bal BS, Managing litigation risk in minimally invasive total joint surgery. AAOS Bulletin. April 2006.
  7. Shon WY, Baldini T, Peterson MG, Wright TM, Salvati EA. Impingement in total hip arthroplasty: A study of retrieved acetabular components. 2005;20:427-435.
  8. Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stöckl B. Reducing the risk of dislocation after total hip arthroplasty. The effect of orientation of the acetabular component. J Bone J Surg Br. 2005;87B:762-769.
  9. D’Lima DD, Urquhart AG, Buehler KO, Walker RH, Colwell CW. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios. J Bone Joint Surg (Am). 2000;82-A:315-321.
  10. Philips et.al. Incidence rates of dislocation, pulmonary embolism and deep infection during the first six months after elective total hip surgery. J Bone Joint Surg. (Am). 2003; 85:20-26.
  11. Morrey BF. Instability after total hip arthroplasty. Orthopedic Clinics of North America. 1992;23:237-248.
  12. Sanchez-Sotelo J, Haidukewych GJ, Boberg CJ. Hospital cost of dislocation after primary total hip arthroplasty. J Bone Joint Surg. 2006; 88-A:290-294.

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