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Zimmer, Inc.

Zimmer® Segmental System

Product Description

The Zimmer® Segmental System is a salvage knee prosthesis intended to replace the distal femur, mid-shaft femur, proximal femur, and/or total knee in cases that require extensive resection and restoration. The Segmental System is also compatible with selected components from NexGen® Rotating Hinge Knee Systems. Using this system it is possible to totally replace the lower limb from the mid-calf to the hip. The distal femoral components are designed to be compatible with NexGen Patella Components.

The Segmental System is a modular system comprised of stem extensions, segments, intercalary segments, articular surfaces and distal femoral components. The components of the Segmental System are made from the following materials:

  • Articular surfaces: UHMWPE and Cobalt-Chromium-Molybdenum Alloy (hinge post)
  • Distal Femoral Components: Cobalt-Chromium-Molybdenum Alloy and Ti-6Al-4V Alloy (set screw)
  • Polyethylene Insert: UHMWPE
  • Segments, Intercalary Segments, and Smooth Stem Collars: Ti-6Al-4V Alloy
  • Stem Extensions: Cobalt-Chromium-Molybdenum Alloy and PMMA
  • Trabecular Metal™ Stem Collars: Tantalum

Unique Trabecular Metal ® Technology

The only salvage system to offer advanced Trabecular Metal Technology — The Best Thing Next to Bone ® . Key features include:

  • Versatility: Trabecular Metal Stem Collars are available in different diameters, thereby increasing intraoperative options
  • Porosity: Up to 85% porosity
  • Flexibility: The 3-D structure provides flexibility
  • Friction/stability: Trabecular Metal Material produces more friction than sintered coatings on cancellous bone

95% Condylar Loading
The Zimmer Segmental System utilizes the same kinematics as the NexGen RH Knee — 95% of the load passes through the condyles, similar to the loading pattern of a primary implant.

  • The femoral component and articular surface are designed to maintain centralized contact throughout the range of motion
  • Reproducing NexGen System kinematics, femoral condyle centering and the shape of the patellar groove allow stable patellar tracking

Transitional Articular Surface
A tapered articular surface allows for increased intraoperative options.

  • Permits the use of a smaller tibial component for a given distal femur size — which is especially advantageous in oncology cases where skin closure can be challenging
  • The articular surface is designed to maintain centralized contact throughout the range of motion

Strong One-Piece Hinge Post
The Segmental One-Piece Hinge Post is designed to provide strong, reliable hinge stability.

  • The one-piece hinge post design eliminates a step in the surgical procedure
  • The one-piece hinge post can be used with the Segmental Distal Femur and can also be used with the NexGen RH Knee Femur
  • To resist subluxation, the mechanism offers a constant "jump height" of at least 40 mm

Anteversion Alignment
An incremental alignment mechanism features tab and pocket adjustment for optimal alignment.

  • Enables reconstruction to more closely match the patient's physiology
  • Allows for controllable adjustment in 20-degree increments

Multiple Unique Stem Options
Stems are available in fluted and splined styles. The fluted styles are available in 130mm and 190mm straight stems and 250mm bowed. The splined press-fit variable stiffness stems are available in 130mm straight and 190mm bowed. Press-fit stems are splined for secure initial press fit with a variable stiffness tip designed to reduce tip stress inside the bone.

Testing and Analysis

Torsional Fatigue Test

  • Testing representing 10 years of stair-climb activity was completed. All segment pairs completed testing without fracture, deformation, or relative rotation between segments.¹ 

Combined Load Test

  • The distal femur was tested to simulate increased hyperextension forces typical of salvage knee cases. After 5 million cycles no fracture or hinge component loosening had occurred.¹

Rotating Hinge Contact Area Analysis

  • The condylar geometry for the Segmental Distal Femur matches that of the NexGen RH Knee¹

Segmental System Stem Test

  • Segmental Stems and cemented Trabecular Metal Material Collars were paired with a MOST Options Proximal Femur and cyclically tested at 7.5 times body weight. The components survived testing without fracture and with no evidence of loosening at the stem/collar interface.¹

Rotary Overhang Fatigue Test

  • Testing was performed to ensure that the tapered articular surfaces display adequate strength and durability. Simulating approximately 20 years of squatting activity, all components survived the testing without fracture, delamination, or excessive deformation.¹

References

  1. Data on file at Zimmer. The results of this testing have not been shown to correlate with clinical mechanisms.
  2. Bobyn JD, Stackpool GJ, Hacking SA, Tanzer M, Krygier JJ. Characteristics of bone in­growth and interface mechanics of a new porous tantalum biomaterial. J Bone Joint Surg Br. 1999;81(5):907-914.
  3. Bobyn JD, Hacking SA, Krygier JJ, Chan SP, Toh KK, Tanzer M. Characterization of a new porous tantalum biomaterial for reconstructive surgery. Scientific exhibition: 66th Annual Meeting of the American Academy of Orthopaedic Surgeons; February 4-8, 1999; Anaheim, CA.
  4. Ward WG, Haight D, Ritchie P, Gordon S, Eckardt JJ. Dislocation of rotating hinge total knee prosthesis. A biomechanical analysis. J Bone Joint Surg Am. 2003; 85-A(3):448-453.

Indications

This device is indicated for:

  • Moderate to severe knee instability
  • Significant bone loss and/or ligament deficiencies caused by neoplasms, trauma, rheumatoid arthritis, osteoarthritis, traumatic arthritis, polyarthritis, collagen disorders, and/or avascular necrosis of the femoral condyle
  • Valgus, varus or flexion deformities
  • The salvage of previously failed surgical attempts

A total femoral replacement construct consisting of MOST Options proximal femoral, Segmental System Segments and Segmental System Distal Femoral Components may be used without cement.

Variable Stiffness stem extensions require the use of either a smooth or Trabecular Metal Stem Collar, which must be cemented to the stem. Following cementing to the stem, the smooth collar must be cemented against the bone, but the remainder of the stem must be used uncemented.

Fluted stem extensions require the use of either a smooth or Trabecular Metal Stem Collar, which must be cemented to the stem. Following cementing to the stem extension, the smooth collar and the remainder of the stem must also be cemented against the bone.

The Trabecular Metal collar may be used cemented or uncemented against the bone.

All other constructs are for cemented use only.

Contraindications

Contraindications include:

  • Local and/or overt infection
  • Insufficient bone stock to allow secure fixation
  • Skeletal immaturity
  • Neuropathic arthropathy
  • Osteoporosis
  • A stable arthrodesis in a satisfactory functional position

Total knee arthroplasty is contraindicated in patients who have rheumatoid arthritis (RA) and an ulcer of the skin or a history of recurrent breakdown of the skin because their risk of postoperative infection is greater.

The Segmental Intercalary Segment is contraindicated for use as a knee fusion device.