Prevention of limb-length discrepancy during THA


"An ounce of prevention is worth a pound of cure..." It may be a centuries old saying but in the case of limb-length discrepancy (LLD) after total hip arthroplasty (THA), it still holds true. This common complication of THA can cause pain, discomfort, and result in dissatisfied patients. (Incidentally, it is the leading cause of litigation against US orthopedic surgeons). Here, we examine a multifaceted approach to preventing LLD. 

 


THA and associated revision surgeries are being performed at increasing rates around the world. A 2014 study of Organisation for Economic Co-operation and Development (OECD) countries looked at THA data between 1990 and 2011 and found that the number of procedures performed annually was increasing seven times faster in the under 64 age group compared to older patients [1]. The researchers also pointed out that there is a strong correlation between a country’s gross domestic product (GDP) and health care spending on the rate of THA. Exponential growth is projected for this procedure.

 

Limb-length discrepancy

Limb-length discrepancy (LLD) is a common complication of THA that can lead to patient dissatisfaction and negatively impact outcomes. It is also the most common cause of litigation against the US orthopedic community and the fourth most common in the UK [2].

 


Lower your risk of litigation by [3]:

  • Documenting everything
  • Being transparent with patients
  • Showing empathy
  • Not being tempted by shortcuts
  • Maintaining open communication and good relationships with patients and their families

Seegert L. 5 strategies to reduce medical malpractice lawsuit threats [3]. Available at: http://medicaleconomics.modernmedicine.com/medical-economics/news/5-strategies-reduce-malpractice-lawsuit-threats


The prevalence of LLD after THA varies greatly and has been reported to be as high as 45 to 50 percent [4, 5]. Most frequently the limb undergoing THA is lengthened [6, 7]. It is generally accepted that an LLD of less than 10 mm is tolerated by patients and this has been suggested as a maximum inequality goal for surgeons performing THA [8]. Interestingly, a 2005 literature review reported that 90 percent of the general population has unequal leg length, with the right leg most often being shorter by, on average, 5.2 mm [9]. Preexisting leg length inequality has been associated with a number of problems, for example, multiple stress fractures in athletes [10], progressive knee osteoarthritis [11], and hip and lumbar degenerative joint disease [12].

Orthopedic surgeon Jurek Pietrzak, based at University College London Hospital, comments that “patients with lifelong leg-length inequality are generally symptom free because of learned adaptive measures, which have evolved naturally.”

 

Impact of LLD after THA

Patients with a LLD of more than 10 mm after THA are more likely to experience lower back pain or sciatica, paresthesia, gait disorders, and hip instability [2, 13], not to mention decreased satisfaction with the procedure. Pietrzak stated that the “sudden, dramatic alteration to what their hip and gait kinematics has become accustomed to, causes a sensation of discomfort, imbalance and lack of control and coordination that may be exacerbated should the offset be altered in addition to limb length.”

Elderly patients with pulmonary, cardiac, or neuromuscular disease have a particularly low tolerance for leg-length inequality due to their compromised physical state [2]. Biju Benjamin, orthopedic surgeon at University College London Hospital points out that “many patients cope perfectly well with some leg-length inequality after surgery but shorter patients and those with stiff spines or pelvic deformity seem to have more difficulty in adjusting.”

There are several pre- and intraoperative considerations that can be implemented to reduce the occurrence of LLD. Woolsen et al obtained a postoperative leg-length difference of less than 10 mm in 97 percent of cases in a study published in 1999 and recommended a multifaceted approach with an emphasis on preoperative templating and planning [14].

 

Preoperative tips for LLD prevention

1. Medical history:

Obtaining a complete medical history to explore local and systemic risk factors is advisable [15]. Better understanding a patient's medical past can help establish reasonable expectations for the procedure for both you and your patient (See Table 1), as well as tease out potential problems that might be encountered operatively or complicate the healing process.

 

Table 1. Local and systemic risk factors to look for when taking a patient’s medical history [16].

 

2. Clinical examination:

A thorough examination will help provide baseline data for a patient's gait, leg length, etc. Careful documentation of your findings is critical for defending decisions should the need arise. There is no single measurement that will deliver a complete picture.

 

Table 2. Clinical examination tests and questions to gather baseline data on leg length before THA [17].

 

3. Radiographic measurements:

To be able to make leg-length measurements on x-rays you need pelvic and femoral reference points/landmarks. An anteroposterior view of the pelvis with both femurs internally rotated approximately 20 degrees is recommended [17]. It is important there is no axial rotation in the pelvis and it should be noted that this approach does not take into account anatomical limb differences below the lessor trochanters.

A 2011 study by Meermans et al found that “the center of the femoral head is a more reliable femoral landmark compared with the lesser trochanter” and the authors “discourage” the use of the biischial line as a pelvic reference while suggesting the interteardrop line as a better alternative [18]. Fig 1 illustrates where these landmarks are located.

 

Figure 1. Landmarks for preoperative templating [18]. An AP x-ray of the pelvis shows the different landmarks marked to measure LLD. CH = center of the femoral head; LT = tip of the lesser trochanter; BI = biischial line; IT = interteardrop line.
With permission:
Meermans G, Malik A, Johan Witt, et al. Preoperative radiographic assessment of limb-length discrepancy in total hip arthroplasty. Clin Orthop Relat Res. 2011 Jun; 469(6):1677–1682.

 

4. Preoperative templating:

Templating is the process of predicting the size and position of implants prior to surgery. Accurate preoperative templating can assist in the selection of implant size and position, guide the femoral osteotomy, and bring back femoral offset to lessen LLD. Clark et al recommends templating the ipsilateral side first to determine acetabular and femoral components [17]. Karadsheh and Incavos suggest templating with the middle range of sizes of your chosen component system; if this doesn’t work a “different system may be a better choice” [19].

 


Steps in THA templating [19]:

  • Obtain appropriate x-rays
  • Record vital patient information on template (age, height, weight, etc)
  • Establish radiographic landmarks
  • Establish limb-length discrepancy
  • Template acetabular component first to determine center of rotation of new hip
  • Template femoral component

With permission: Karadsheh M, Incavo S. THA Templating. OrthoBullets. Available at: http://www.orthobullets.com/recon/12124/tha-templating.


In the May 2017 issue of Orthopaedics & Traumatology: Surgery and Research, Wang et al published a paper highlighting their combination of “the traditional manual templating with standing digital radiograph calibrated by a scaling ball” to cost-effectively overcome the issue of manufacturer templates not working with amplification ratios of acetate x-ray films [20].

Clark et alremind us that templates need to be used in combination with a “reliable intraoperative method to obtain optimal length” [17].

 

5. Managing patient expectations:

Hutson et al found that patients are more likely to remember information about the potential benefits of THA than preoperative information about risks and expectations. In fact, even after patient education and consent has occurred, close to half of patients that ended up with LLD did not remember being told about this as a potential complication [21]. Surgeons need to clearly establish and confirm understanding, stressing that equal leg lengths are not guaranteed. Shortening may be inevitable, as may lengthening in the pursuit of stability; each case is different [17]. Biju Benjamin, orthopedic surgeon, advises that “the key to managing patient expectations is explaining that there is always a decision to be made between getting the hips stable and functional, and getting length absolutely right.”

 

Tips for intraoperative prevention of LLD

Careful and thorough preoperative planning is a critical step in preventing LLD after THA, but there are also intraoperative considerations that can help minimize it. Close to 20 different techniques have been described in the literature to help correct LLD during THA. Desai et al note that they all “use a stable pelvic reference point and a variable femoral reference” [2].

Anatomical landmarks identified during templating and preoperative measurements are used intraoperatively to help assess trial prostheses placement before finalizing sizing and securing the implant components [17].

 

1. Implant positioning:

Patient positioning impacts measurements and landmarking during THA. Clark et al suggests patients should be positioned in a manner that allows for orientation of identified external and internal landmarks, with the surgeon checking that the contralateral limb can be palpated through the draping [17]. It can be challenging to balance prosthesis selection with soft tissue tension, stability, and LLD [17].

There has been some evidence that improved accuracy in acetabular placement was obtained by surgical teams using computer/robot assisted surgery, but their outcomes were measured against dislocation rates not LLD [22].

There are several intraoperative actions that directly impact leg length. LLD can be adversely impacted by, but not limited to:

  1. The acetabulum undergoing eccentric inferior reaming and the cup placed below
    the planned level of the teardrop [17]
  2. Mismatch of the metaphyseal-medullary canal [23]
  3. Inaccurate femoral neck osteotomy that impacts femoral stem seating
  4. An increase in femoral neck length to return soft-tissue tension [15].

 

2. Soft-tissue considerations:

It is widely acknowledged that intraoperative assessment of soft tissue and balancing help preserve tissue tension and stability in the hip joint. It should be noted that soft tissues are impacted by the type of anesthetic used and preoperative contractures [9, 19]. There are several recommended intraoperative tests that can be used to assess soft tissues, see Fig 2. Tests are repeated until desired leg length is achieved, with implant size and brand being fine-tuned during this phase.

 

Figure 2. Compiled from [9, 18, 19].

 

3. Intraoperative leg-length assessment:

It can be difficult for even experienced surgeons to evaluate leg lengths intraoperatively, but restoration of practical leg lengths may be more successful if multiple assessment methods are employed during surgery [24]. Manual methods are most common and include, but are not limited to [5, 18, 19, 25-27]:

  • Mechanical pins (including Steinmann pin)
  • Osteotomy
  • Tissue tensioning
  • Placement of landmark suture in skin and diathermy point marked for measurement and comparison of suture tail
  • Vertical and horizontal caliper measurements
  • Computer navigation
  • In situ arthroplasty
  • Abductor shuck
  • Patella electrocardiogram leads

However, inaccuracies can occur as flexion contracture and patient positioning inconsistencies introduce error. Inaccurate abduction/adduction repositioning of the femur by 5 degrees resulted in 8 mm of apparent change in leg length in a study by Rice et al [27].

 

Conclusion

It can be challenging for even the most experienced surgeons to assess leg length during THA. However, through careful collection of a patient's medical history, preoperative planning and templating, and the use of multiple intraoperative assessments, the risk of LLD over 10 mm after THA can be reduced.

 

Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

Biju Benjamin MD

University College
London Hospital
London, United Kingdom

Babar Kayani MD

University College
London Hospital
London, United Kingdom

Jurek Pietrzak MD

University College
London Hospital
London, United Kingdom

This issue was created by Word+Vision Media Productions, Switzerland

 

Additional Resources

Additional AO resources

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References

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