Orthopedics

The Dislocator, Early and Late: The Role of Large Heads

Michael D. Skeels, DO; Keith R. Berend, MD; Adolph V. Lombardi Jr., MD

Abstract

Dislocation after total hip arthroplasty (THA) is a potentially devastating complication that can be difficult to manage. Many patient and mechanical factors have been associated with an increased risk of dislocation. Conservative treatments such as abduction bracing have not proven effective at treating this difficult problem. Surgical options include the use of larger femoral heads, unconstrained tripolar femoral heads, and constrained devices. While each device has its merits, there is no one-size-fits-all solution to this problem. With the development of highly cross-linked polyethylene and its superior wear characteristics and mechanical properties, the use of larger femoral heads is now available.

Twenty-six hips in 25 patients who underwent revision surgery for recurrent dislocation were treated with a femoral head >36 mm in diameter. The direct lateral surgical approach was used in 24 hips, and the posterior and anterior supine intermuscular approaches were used in 1 hip each. One patient died 5 years after revision surgery, and 3 patients have not returned for clinical follow-up over the past 2 years. Four hips subsequently suffered a repeat dislocation, for a dislocation rate of 17%. Two patients underwent a subsequent surgery: 1 irrigation and debridement and 1 hardware removal. There have been no other revisions to date. Mean time to follow-up is 17.2 months. While the use of large femoral heads for the treatment of dislocation is warranted, continued follow-up is necessary.

Dislocation is an all-too-common complication of total hip arthroplasty (THA), with a 3.9% incidence in primary THA and between 7.4% and 14.4% in revision THA.1,2 Additionally, it has been reported that 22.5% of all hip revisions are due to instability or dislocation.3 Numerous patient factors have been cited as contributing to an increased risk of dislocation, such as previous femoral neck fracture, age, sex, neuromuscular disorder, cognitive function, hip dysplasia, and rheumatoid arthritis.4,5 Mechanical factors such as inadequate soft tissue tension, implant design and position, and bone and soft tissue impingement have also been identified as risk factors for dislocation.6,7

It has been shown that accuracy of the acetabular component with placement of the component in the safe zone of 45° abduction and 15° anteversion is critical for the prevention of dislocation.7,8 Accurate placement can be difficult to achieve, with one study reporting 42% of acetabular components outside the safe zone.9

Advances in polyethylene are now allowing surgeons to use larger femoral heads, resulting in a substantial increase in stability.10 Larger femoral heads offer the advantage of increasing the jump distance required for dislocation while also giving the patient greater range of motion (ROM).11

The treatment of postoperative dislocation is a challenge that surgeons have been addressing for years. Abduction bracing following closed reduction has been shown to be ineffective in preventing repeat dislocation.12 Sixty-one percent of patients treated with abduction bracing following initial dislocation sustained a repeat dislocation vs 64% of patients treated without bracing, at a mean follow-up of 4 years. Fifty-five percent of patients treated with abduction bracing for recurrent dislocation sustained a recurrent dislocation vs 56% of patients treated without bracing, at mean follow-up of 3.7 years. Various component options such as unconstrained tripolar implants and constrained implants are valuable tools available to the surgeon when conservative treatments have failed.

Institutional review board permission was obtained for a retrospective review of all patients who underwent revision THA for recurrent dislocation and treated with unconstrained femoral heads >36 mm. Our electronic database identified 26 hips in 25 patients that had undergone this procedure. One patient died 4.9 years after revision surgery. Mean patient age at the time of revision surgery was 61.3 years (range, 41-91 years). Thirteen left hips…

Dislocation after total hip arthroplasty (THA) is a potentially devastating complication that can be difficult to manage. Many patient and mechanical factors have been associated with an increased risk of dislocation. Conservative treatments such as abduction bracing have not proven effective at treating this difficult problem. Surgical options include the use of larger femoral heads, unconstrained tripolar femoral heads, and constrained devices. While each device has its merits, there is no one-size-fits-all solution to this problem. With the development of highly cross-linked polyethylene and its superior wear characteristics and mechanical properties, the use of larger femoral heads is now available.

Twenty-six hips in 25 patients who underwent revision surgery for recurrent dislocation were treated with a femoral head >36 mm in diameter. The direct lateral surgical approach was used in 24 hips, and the posterior and anterior supine intermuscular approaches were used in 1 hip each. One patient died 5 years after revision surgery, and 3 patients have not returned for clinical follow-up over the past 2 years. Four hips subsequently suffered a repeat dislocation, for a dislocation rate of 17%. Two patients underwent a subsequent surgery: 1 irrigation and debridement and 1 hardware removal. There have been no other revisions to date. Mean time to follow-up is 17.2 months. While the use of large femoral heads for the treatment of dislocation is warranted, continued follow-up is necessary.

Dislocation is an all-too-common complication of total hip arthroplasty (THA), with a 3.9% incidence in primary THA and between 7.4% and 14.4% in revision THA.1,2 Additionally, it has been reported that 22.5% of all hip revisions are due to instability or dislocation.3 Numerous patient factors have been cited as contributing to an increased risk of dislocation, such as previous femoral neck fracture, age, sex, neuromuscular disorder, cognitive function, hip dysplasia, and rheumatoid arthritis.4,5 Mechanical factors such as inadequate soft tissue tension, implant design and position, and bone and soft tissue impingement have also been identified as risk factors for dislocation.6,7

It has been shown that accuracy of the acetabular component with placement of the component in the safe zone of 45° abduction and 15° anteversion is critical for the prevention of dislocation.7,8 Accurate placement can be difficult to achieve, with one study reporting 42% of acetabular components outside the safe zone.9

Advances in polyethylene are now allowing surgeons to use larger femoral heads, resulting in a substantial increase in stability.10 Larger femoral heads offer the advantage of increasing the jump distance required for dislocation while also giving the patient greater range of motion (ROM).11

The treatment of postoperative dislocation is a challenge that surgeons have been addressing for years. Abduction bracing following closed reduction has been shown to be ineffective in preventing repeat dislocation.12 Sixty-one percent of patients treated with abduction bracing following initial dislocation sustained a repeat dislocation vs 64% of patients treated without bracing, at a mean follow-up of 4 years. Fifty-five percent of patients treated with abduction bracing for recurrent dislocation sustained a recurrent dislocation vs 56% of patients treated without bracing, at mean follow-up of 3.7 years. Various component options such as unconstrained tripolar implants and constrained implants are valuable tools available to the surgeon when conservative treatments have failed.

Materials and Methods

Institutional review board permission was obtained for a retrospective review of all patients who underwent revision THA for recurrent dislocation and treated with unconstrained femoral heads >36 mm. Our electronic database identified 26 hips in 25 patients that had undergone this procedure. One patient died 4.9 years after revision surgery. Mean patient age at the time of revision surgery was 61.3 years (range, 41-91 years). Thirteen left hips and 13 right hips of 13 men and 12 women were involved. Three patients have not returned for clinical follow-up over the past 2 years and are considered lost to follow-up. The direct lateral surgical approach was used in 24 hips, and the posterior and anterior supine intermuscular approaches were used in 1 hip each. Revision surgery consisted of liner exchange with retention of the acetabular component in 6 hips and revision of the acetabular component in 20 hips (Figures 1-3).

Figure 1: Radiograph of a 54-year-old man 3 months post-staged right THA

Figure 1: Radiograph of a 54-year-old man 3 months post-staged right THA secondary to alcohol-related avascular necrosis from an outside institution. The patient had previously dislocated 3 times and underwent closed reduction and abduction bracing.


Figure 2: A revision procedure with retention of the acetabular and femoral components

Figure 2: Radiograph of the same patient after subsequently undergoing a revision procedure with retention of the acetabular and femoral components. The femoral head was exchanged and a 40-mm outer diameter unconstrained tripolar head was used.


Figure 3: The poor positioning of the acetabular component was addressed with an acetabular revision and conversion to a constrained device

Figure 3: Radiograph of the same patient after undergoing another revision. The poor positioning of the acetabular component was addressed with an acetabular revision and conversion to a constrained device.

Results

Mean time to follow-up was 17.2 months for patients with no subsequent dislocation. Average femoral head diameter was 37.5 mm, with 15 cases receiving 36 mm, 2 cases receiving 38 mm, and 9 cases receiving 40 mm. Two patients required a subsequent surgery: 1 irrigation and debridement for persistent wound drainage and 1 hardware removal. Four patients sustained a repeat dislocation at an average of 2.3 months (range, 0 days to 6 months), resulting in a 17% redislocation rate.

Discussion

The treatment of postoperative dislocation after primary THA is a complicated problem with no clear solution. It is clear that abduction bracing is not a reliable solution, and surgical management is a complex and technically demanding solution with variable rates of success. Surgical options include large femoral heads, unconstrained tripolar implants, and constrained devices.

The use of large heads in primary and revision THA allows for a hip that has greater ROM and increased stability when compared to smaller femoral heads.11 The superior wear characteristics and improved mechanical properties of highly cross-linked polyethylene have allowed the use of larger-diameter femoral heads.10 A larger head size allows the patient greater ROM until mechanical impingement and an increased jump distance required for dislocation, thereby providing enhanced stability. In a report of patients who underwent a revision THA with 36- and 28-mm heads and an intact abductor mechanism, the hips implanted with 36-mm heads had no dislocations and the hips with 28-mm heads had a dislocation rate of 12.7%.13

Unconstrained tripolar implants are another option that gives the patient increased stability with the use of a large femoral head. This articulation was introduced in the mid-1980s and is a bipolar femoral prosthesis that articulates with a standard THA acetabular component. One study on this device reported that 65% of patients were revised for previous instability and the remaining were implanted with the device when they were deemed unstable at the time of revision surgery.14 A dislocation rate of 10% occurred at a minimum 24-month follow-up.

Constrained devices are indicated when there is severe abductor deficiency, multidirectional hip instability, and recurrent dislocation with properly oriented components. When using constrained devices, the components need to be properly orientated. Various reports have established the success of these devices, but they are not without potential complications such as redislocation, aseptic loosening, and premature polyethylene wear.15

Prevention is of the utmost importance in regards to postoperative dislocation. The acetabular component needs to be in the optimal position; consider using large femoral heads. A meticulous soft tissue repair is also important. If a patient subsequently experiences a postoperative dislocation, a trial of closed reduction may be warranted. If the patient dislocates again after a trial of closed reduction, a revision may be required to achieve implant stability. Consider liner exchange only if the acetabular component is well fixed and well positioned. Also to be considered is the use of large femoral heads, the tripolar articulation, and finally constrained devices.

References

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  2. Phillips CB, Barrett JA, Losina E, et al. Incidence rates of dislocation, pulmonary embolism, and deep infection during the first six months after elective total hip replacement. J Bone Joint Surg Am. 2003; 85(1):20-26.
  3. Bozic KJ, Kurtz SM, Lau E, Ohg K, Vail TP, Berry DJ. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am. 2009; 91(1):128-133.
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  11. Bader R, Scholz R, Steinhauser E, Zimmermann S, Busch R, Mittelmeier W. The influence of head and neck geometry on stability of total hip replacement: a mechanical test study. Acta Orthop Scand. 2004; 75(4):415-421.
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  15. Berend KR, Lombardi AV Jr, Welch M, Adams JB. A constrained device with increased range of motion prevents early dislocation. Clin Orthop Relat Res. 2006; (447):70-75.

Authors

Drs Skeels, Berend, and Lombardi are from Joint Implant Surgeons, Inc, the Ohio State University, Mount Carmel Health Systems, New Albany, Ohio.

Dr Skeels has no relevant financial relationships to disclose. Drs Berend and Lombardi receive royalties from, are paid consultants and speakers for, and receive research or institutional support from Biomet, and Dr Lombardi also receives royalties from Innomed.

Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.

Correspondence should be addressed to: Keith R. Berend, MD, Mt Carmel New Albany Surgical Hospital, 7277 Smith’s Mill Rd, Ste 200, New Albany, OH 43054.

DOI: 10.3928/01477447-20090728-14

10.3928/01477447-20090728-14

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