Surgical Considerations for Preventing Dislocation after THA
At ICJR’s Pan Pacific Orthopaedic Congress, Dr. Adolph Lombardi shared his thoughts on what orthopaedic surgeons can do to help minimize the risk that a patient will dislocate after a total hip arthroplasty. Below is the abstract of his presentation.
By Adolph V. Lombardi Jr., MD, FACS
Dislocation after total hip arthroplasty 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. Options to reduce the risk include the use of:
- Larger femoral heads
- Unconstrained tripolar femoral heads
- Dual-mobility designs
- Newer constrained devices
Advances in bearings have expanded prosthetic head options from traditional sizes to diameters as large as 60 mm. Larger heads enhance stability secondary to increased range of motion before impingement and increased jump distance prior to subluxation. [1,2]
Risk factors for dislocation can be categorized as impingement-independent and impingement-related.
Impingement-independent factors involve compromise of soft tissue tension and may be related to:
- Insufficient offset
- Improper position of the hip center
- Insufficient tissue balance
- Trochanteric avulsion
- Compromised abductor muscle
- Inadequate soft tissue closure
Patient-specific factors include:
- Neurologic disorders
- Advanced age
- Diagnosis, such as developmental dysplasia and rheumatoid arthritis
- Number of previous surgeries
- Non-compliant patient behavior
- Substance abuse
Although the posterior approach has been associated with a higher rate of dislocation versus the direct lateral approach, the incidence has markedly decreased with current emphasis on repair of the posterior capsular structures. The direct lateral approach (the author’s preference) has the advantage of improved visualization of the acetabulum and femur without the compromising the posterior capsular structures that are integral to the stability of the hip. [1,3,4]
Impingement-related risk factors for dislocation can be subdivided into several groups.
- While larger heads have been shown to decrease incidence of dislocation, head-to-neck ratio may be more important. Inadequate head-to-neck ratio produces impingement. Considering a standard neck length in a 7° included angle taper, range of motion prior to impingement increases from 127.4° for a 28-mm head to 138.62° for a 36-mm head.
- Additionally, the taper geometry has an effect on range of motion. A 36-mm head with a 7° included angle taper will allow 138.6° range of motion prior to impingement, while the same head size with 12/14 allows 132.09°.
Other factors in minimizing impingement include the following:
- A neck design with flat sides or a trapezoidal shape enhances range of motion prior to impingement.
- A long versus short neck is advantageous for minimizing bony impingement.
- Acetabular liners without high walls or labrums decrease impingement
Optimization of femoral and acetabular component position can also decrease impingement. Restoration of proper offset and removal of osteophytes can prevent bone and soft tissue impingement.
A thorough evaluation of the soft tissues is warranted because a tenuous or stretched abductor mechanism increases the risk of dislocation. Prosthetic stability can be enhanced by positioning the acetabular component in a reduced, more horizontal angle of inclination. A constrained acetabular component or a snap-fit cup with an extended labrum can also be helpful when dislocation potential is increased.
The effectiveness of such intraoperative technical modifications can be enhanced by modifying the postoperative rehabilitation program to include the use of an abduction orthosis.
At the time of component reduction, the surgeon must make final determinations with respect to stability and leg length. Optimally, the acetabulum should be reconstructed to maintain the anatomic hip center and the femur should be reconstructed to restore its anatomic length. When dealing with the issue of hip stability versus leg length, the surgeon should always opt for stability:
- If a trochanteric osteotomy has been performed, stability may be enhanced by advancement of the trochanteric fragment.
- If a posterolateral approach has been used, attempts should be made to repair the short external rotators.
- If the direct lateral approach has been used, meticulous approximation of the myofascial sleeve should be done.
Postoperative management is dictated by the extent of surgical reconstruction performed. Stability, as assessed at reduction, is critical in determining need for a hip abduction orthosis during initial physical therapy and rehabilitation.
The physical therapist should be apprised of concerns regarding stability and instruct the patient with respect to hip precautions, such as avoiding prolonged sitting in a chair and learning techniques for rising from a toilet, climbing stairs, and riding in a car.
If a trochanteric osteotomy was performed, there should be appropriate delay in commencing hip abduction exercises.
With respect to dislocation, prevention is the best treatment and paramount to avoiding this complication:
- Respect the soft tissue envelope about the hip in every primary and revision arthroplasty.
- Optimize component position and orientation.
- Restore offset and leg length to help restore soft tissue balance and tension.
- Use large femoral heads with reduced tapered geometries to enhance range of motion prior to impingement, which diminishes the incidence of dislocation.
Constrained liners may be indicated, but represent a necessary evil and should be used with caution. Our disappointing experience with the S-ROM Poly-Dial constrained liner has led us to explore newer designs. [5,6]
Several newer designs are approved for use in the US. One particular design used in our practice allows constraint of a 36-mm head.  Therefore, the range of motion prior to impingement varies from 109° to 114°, a significant enhancement over previous designs. Results have improved with the introduction of newer designs. 
Adolph V. Lombardi Jr., MD, FACS, is from Joint Implant Surgeons, Inc.; The Ohio State University Wexner Medical Center; and Mount Carmel Health Systems, New Albany, Ohio.
- Lombardi AV Jr, Skeels MD, Berend KR, Adams JB, Franchi OJ. Do large heads enhance stability and restore native anatomy in primary total hip arthroplasty? Clin Orthop Relat Res. 2011 Jun;469(6):1547-53.
- Skeels MD, Berend KR, Lombardi AV Jr. The dislocator, early and late: the role of large heads. Orthopedics. 2009 Sep;32(9). pii: orthosupersite.com/view.asp?rID=42837. doi: 10.3928/01477447-20090728-14.
- Mallory TH, Lombardi AV, Fada RA, Herrington SM, Eberle RW: Dislocation after total hip arthroplasty using the anterolateral abductor splitting approach. Clin Orthop Relat Res. 1999; 358:166-172.
- Smith TM, Berend KR, Lombardi AV Jr, Mallory TH, Russell JH: Isolated liner exchange using the anterolateral approach is associated with a low risk of dislocation. Clin Orthop Relat Res. 2005 Dec; 441:221-226.
- Berend KR, Lombardi AV Jr; Mallory TH, Adams JB, Russell JH, Groseth KL. The long-term outcome of 755 consecutive constrained acetabular components in total hip arthroplasty: Examining the successes and failures. J Arthroplasty. 2005 Oct; 20(6 Suppl 3):93-102.
- 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 June;447:70-75.