Orthopedics

Case Report 

Atraumatic Fracture of Cemented Vanguard Total Knee Arthroplasty Femoral Component

Tyler J. Vovos, MD; Tyler S. Watters, MD; Erin M. Hughes, FNP; David C. McNabb, MD

Abstract

The authors report the case of an atraumatic femoral component fracture 10 years after primary total knee arthroplasty (TKA) with a modern cemented fixed bearing system. The patient, a 70-year-old man, had the complication without inciting trauma, and he subsequently had severe pain and disability. This rare mode of TKA failure occurred at the superolateral aspect of the femoral component’s anterior flange. At the time of revision, no femoral osteolysis was seen and the backside of the prosthesis fracture fragment was found to be free of cement. To the authors’ knowledge, this is the first case of femoral component fracture in a Vanguard TKA (Biomet, Warsaw, Indiana), and the first case of fracture in a modern cobalt-chrome alloy femoral component associated with aseptic cement debonding. Femoral component stress fracture is a rare but serious complication of TKA. Reports of femoral component fracture in early designs were attributed to geometric design flaws, whereas modern TKA designs appear to fail when ingrowth failure, aseptic debonding, or osteolysis result in inadequate bony support of the prosthesis. Careful attention to bone cuts in porous-coated uncemented TKA systems and proper cementing technique in cemented TKA systems may preclude this rare complication. In the case of severe osteolysis, early revision may prevent catastrophic implant failure. [Orthopedics. 2020;43(5):e476–e479.]

Abstract

The authors report the case of an atraumatic femoral component fracture 10 years after primary total knee arthroplasty (TKA) with a modern cemented fixed bearing system. The patient, a 70-year-old man, had the complication without inciting trauma, and he subsequently had severe pain and disability. This rare mode of TKA failure occurred at the superolateral aspect of the femoral component’s anterior flange. At the time of revision, no femoral osteolysis was seen and the backside of the prosthesis fracture fragment was found to be free of cement. To the authors’ knowledge, this is the first case of femoral component fracture in a Vanguard TKA (Biomet, Warsaw, Indiana), and the first case of fracture in a modern cobalt-chrome alloy femoral component associated with aseptic cement debonding. Femoral component stress fracture is a rare but serious complication of TKA. Reports of femoral component fracture in early designs were attributed to geometric design flaws, whereas modern TKA designs appear to fail when ingrowth failure, aseptic debonding, or osteolysis result in inadequate bony support of the prosthesis. Careful attention to bone cuts in porous-coated uncemented TKA systems and proper cementing technique in cemented TKA systems may preclude this rare complication. In the case of severe osteolysis, early revision may prevent catastrophic implant failure. [Orthopedics. 2020;43(5):e476–e479.]

Femoral component fracture is a rare mode of failure for total knee arthroplasty (TKA).1–12 Reports of femoral component fracture in early designs were attributed to implant design flaws, such as in the Whiteside Ortholoc II prosthesis (Dow Corning Wright).6–9,11 Despite great advancements in TKA implant design and materials in recent decades, femoral component fracture has also been reported in modern TKA designs. The exact etiology of femoral component fracture in modern implants is unclear, but the available literature suggests that failure occurs through a fatigue mechanism in the setting of osteolysis, aseptic debonding, and/or ingrowth failure, which result in inadequate bony support of the prosthesis.

The Vanguard total knee system (Biomet, Warsaw, Indiana) is a modern implant that was developed to improve upon the Anatomical Graduated Component implant (Biomet). The Vanguard prosthesis has subsequently had a relatively good track record, with studies showing 98.6% and 98.4% survival at 6 and 10 years, respectively, and a rate of aseptic loosening of the femoral component as low as 0.06% (1 of 1674) at 10 years.13,14

The authors report the first case of femoral component fracture in a Vanguard TKA, and the first case of fracture in a cobalt-chrome alloy femoral component associated with aseptic cement debonding.

Case Report

History, Physical Examination, and Radiographs

In 2008, a 70-year-old man underwent left TKA for end-stage left knee osteoarthritis using a cemented Vanguard posterior stabilized TKA at another institution. He had an uncomplicated postoperative course and returned to full function shortly after surgery. In 2013, he presented to the authors with right knee pain in the setting of osteoarthritis (Figure 1) and subsequently underwent uncomplicated right TKA. At this time, his left TKA appeared well fixed and aligned. However, radiographs from another institution and a lateral view of the left knee prosthesis were not available for review, so the appearance of the femoral component–cement interface could not be retrospectively evaluated.

Anteroposterior (A) and merchant (B) views in 2013 demonstrating right knee osteoarthritis and left total knee arthroplasty with expected well-fixed, well-aligned appearance.

Figure 1:

Anteroposterior (A) and merchant (B) views in 2013 demonstrating right knee osteoarthritis and left total knee arthroplasty with expected well-fixed, well-aligned appearance.

In May 2018, 10 years after primary left TKA, he developed acute-onset left knee pain and swelling without inciting trauma. His symptoms subsided during 1 to 2 days without treatment. Two months later, he was evaluated at his local emergency department. Plain radiographs demonstrated fracture of the left TKA femoral component, prompting referral back to the authors. On presentation, he was unable to sit, stand, or bear weight comfortably. On examination, he was 69 inches tall and weighed 274 pounds (body mass index, 40.5 kg/m2). He had a palpable effusion and global tenderness, with maximal tenderness along the superomedial knee. A 5° extension lag was present and active flexion was limited to 45°. There was no varus or valgus instability of the knee.

Radiographs demonstrated a fracture of the superolateral anterior flange of the femoral component with a free metal fragment seated along the medial aspect of the medial femoral condyle (Figure 2). Sterile aspiration of the knee resulted in evacuation of 55 mL of bloody fluid. This fluid was sent for culture and sensitivity, Gram stain, cell count, and alpha-defensin testing to rule out infection.

Anteroposterior (A), lateral (B), and merchant (C) views at the preoperative visit demonstrating fracture of the superolateral anterior flange of the femoral component with free-floating metal fragment seated along the medial aspect of the medial femoral condyle.

Figure 2:

Anteroposterior (A), lateral (B), and merchant (C) views at the preoperative visit demonstrating fracture of the superolateral anterior flange of the femoral component with free-floating metal fragment seated along the medial aspect of the medial femoral condyle.

Surgical Procedure

The patient underwent revision of the femoral component in July 2018. At the time of arthrotomy, a large hemarthrosis was encountered. The fractured superolateral anterior flange of the femoral component was readily visualized (Figure 3A). Inspection of the patellar component revealed significant wear and excoriation, predominately at its lateral aspect (Figure 3B). The free-floating metal fragment seated in the medial gutter was easily extracted, and no cement was seen on the backside of the fragment (Figures 3C–D). Loose plastic fragments were appreciated in the peripatellar region and suprapatellar pouch. The femoral component was removed without significant bone loss, and there was no evidence of osteolysis. The femur was prepared, and a Vanguard 360 revision femoral component was inserted and fixed with cement. The patellar component was revised, and a posterior stabilized tibial insert was replaced. The knee was balanced in flexion and extension and the patella tracked centrally throughout range of motion.

Anterolateral view of the fractured femoral anterior flange (A), patellar component with significant central lateral wear (B), and explanted femoral component with retrieved metal fragment (C, D).

Figure 3:

Anterolateral view of the fractured femoral anterior flange (A), patellar component with significant central lateral wear (B), and explanted femoral component with retrieved metal fragment (C, D).

Follow-up

No complications were noted postoperatively. At 6 weeks postoperatively, the patient had improved quadriceps strength and was walking without an assistive device, with radiographs demonstrating well-fixed revision components (Figure 4). At 3-month follow-up, the patient had minimal pain, range of motion was 2° to 110° without an extensor lag, the knee was stable with varus/valgus stress, and there was excellent patellar tracking.

Anteroposterior (A), lateral (B), and merchant (C) views at 6 weeks after the revision visit demonstrating revised femoral and patellar components and retained tibial component.

Figure 4:

Anteroposterior (A), lateral (B), and merchant (C) views at 6 weeks after the revision visit demonstrating revised femoral and patellar components and retained tibial component.

Discussion

Femoral component fracture after TKA is a rare complication, with few case reports in the literature.1–12 Metallurgical studies on retrieved implants suggest that component fracture typically occurs by a fatigue mechanism.1,6,8,9 Fatigue fracture can occur in any metal structure repeatedly loaded at high enough stress for a sufficient number of cycles.9 When deficient bony support underlies a portion of a TKA implant, that portion of the implant can function as a cantilever, resulting in repetitive stress at the interface with the remaining well-supported prosthesis.15

Reports of femoral component fracture in early TKA designs were attributed to implant design flaws, most notably in the Whiteside Ortholoc II prosthesis, where fractures occurred at the thin transition region (<2 mm) between the distal most surface and the adjacent posterior 45° bevel surface of the femoral component.6–9,11 In modern mobile bearing1–3,12 and fixed bearing prostheses,4,5,10 inadequate bony support of the implant has been thought to be the driving force for fatigue failure, more so than the prosthesis design. Specifically, fractures have been attributed to failure of bone ingrowth in cementless PFC (DePuy)10 and Genesis II (Smith & Nephew)5 TKAs and to osteolysis in Genesis II4 and both cemented1 and uncemented2,3 LCS design TKAs (DePuy).

Cementless fixation and component design appear to be associated with risk for component fracture, as 18 of 24 (75%) of the reported cases have involved uncemented components. As mentioned, failure in uncemented components can occur in the setting of ingrowth failure.5,10 However, uncemented components may also have a decrease in alloy strength of 16% due to the sintering process and notch sensitivity at the interface between the porous layer and solid substrate.16,17

Aseptic debonding is a potential cause of early loosening in modern cemented TKA designs18,19 and may also contribute to fatigue failure. Recently, Park et al12 reported a case of femoral component fracture in a cemented B-P TKA (Endotec) manufactured from titanium alloy and were the first to suggest aseptic debonding of the cemented femoral component as the cause for fatigue fracture. The current case also had evidence of cement debonding behind the anterior flange, possibly due to poor cementation technique. The authors believe that this debonding may have contributed to component fracture through the fatigue mechanism described above. Additionally, the preinjury radiograph merchant view and retrieved patella component suggested chronic overloading of the lateral flange of the femoral component, which may have further contributed to the failure. To the current authors’ knowledge, there have been no prior reports of femoral component fracture secondary to cement debonding in components made of cobalt-chrome alloy, as seen in the current case.

Conclusion

Femoral component stress fracture is a rare but serious complication of TKA. Studies on retrieved implants suggest that component fracture typically occurs by a fatigue mechanism.1,6,8,9 Reports of femoral component fracture in early designs have been attributed to geometric implant design flaws, whereas modern TKA designs appear to fracture in the setting of aseptic debonding, osteolysis, and/or in-growth failure, which result in inadequate bony support of the prosthesis. Careful attention to bone cuts in porous-coated uncemented TKA systems and proper cementing technique in cemented TKA systems may preclude this rare complication. In the case of severe osteolysis, early revision may prevent catastrophic implant failure.

References

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Authors

The authors are from the Department of Orthopaedic Surgery (TJV), Duke University Medical Center, Durham, and Raleigh Orthopaedic Clinic (TSW, EMH, DCM), Raleigh, North Carolina.

Dr Vovos, Ms Hughes, and Dr McNabb have no relevant financial relationships to disclose. Dr Watters is a paid consultant for Total Joint Orthopaedics.

Correspondence should be addressed to: Tyler J. Vovos, MD, Department of Orthopaedic Surgery, Duke University Medical Center, Box 3000, Durham, NC 27710 ( Tyler.Vovos@duke.edu).

Received: July 29, 2019
Accepted: October 14, 2019
Posted Online: August 06, 2020

10.3928/01477447-20200721-07

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