Minimally Invasive Total Hip Arthroplasty

What you need to know…

There is a lot of discussion about “minimally invasive total hip arthroplasty” (MISTHA) – in the media, on the internet, at orthopaedic industry meetings, and at orthopaedic surgeon meetings, but what is MISTHA? What are the possible benefits; is it better than conventional total hip arthroplasty? What are the possible problems? What does recent research tell us about MISTHA? This tutorial will answer these questions without presenting an advocacy or skeptical viewpoint.

What is MISTHA?

As of yet, there is no single, standard definition for MISTHA. At least one author has suggested that “minimally invasive” is a misnomer and should be discarded. After all, regardless of the incision size, the acetabulum must be reamed, the femoral head removed, and the femoral canal reamed to prepare for implantation. These actions can hardly be classified as minimally invasive. Other, more descriptive, nomenclature has been suggested: minimal-incision, limited-incision, and less-invasive total hip arthroplasty (THA). In essence, there are a variety of THA procedures with varying incision lengths, incision placements, surgical approaches, and underlying tissue dissection; for simplicity, all of these are referred to as MISTHA in this tutorial.

The primary goal of any surgical innovation is to improve upon the standard surgical procedure, or at the very least to produce results “as good as” what is currently being offered. MISTHA seeks to do this primarily by using smaller incisions and by causing less soft tissue damage under the skin.

Basically, MISTHA procedures can be classified by the number of incisions: one or two. Single incision techniques are usually either posterior-approach or anterior-approach, and incision lengths vary from 2.5 to 5.5 inches (6 to 14 cm). The two-incision technique uses two smaller incisions, 1 to 2 inches (2.5 to 5 cm) in length, one for placement of the acetabular component, the other for insertion of the femoral component. For comparison, a standard THA incision length varies from 5 to 14 inches (13 to 36 cm), with contemporary incisions on the lower end of the range. There is also the difference between cosmetic MISTHA (small incision with standard dissection) and functional MISTHA (small incision with minimal soft tissue disruption).

Incision Lengths

  • Single-incision MISTHA @ 2.5 to 5.5″ (6 to 14 cm)
  • Two-incision MISTHA @ 1 to 2″ (2.5 to 5 cm)
  • Standard THA @ 5 to 14″ (13 to 36 cm)

MISTHA procedures require surgical skill sets different from standard THA. Not only is the surgical field of view reduced, but because minimizing soft tissue disruption is a primary goal of MISTHA, the navigation is different. To meet this primary goal, instruments must be redesigned. Retractors, oscillating saws, acetabular reamers, and femoral instruments must accommodate the smaller and deeper surgical field though changes in length, angle, and handle design. Ideally, component design also changes for the same reasons. And, since the field of view is reduced, some MISTHA procedures utilize imaging techniques to assist in navigation.

What are the possible benefits of MISTHA?

Most of the expected benefits from MISTHA arise from reduced soft tissue damage as compared to standard THA. Reduced intraoperative blood loss and reduced postoperative pain are direct benefits expected from reduced soft tissue damage. Secondary benefits include quicker recovery, shorter hospital stays, reduced hospital-associated costs, faster return to normal activity, and improved clinical outcomes. Other purported benefits arise from improved scar appearance (improved cosmesis) and greater patient satisfaction.

Expected Benefits of MISTHA

  • Reduced postoperative pain,
  • Reduced blood loss,
  • Quicker recovery,
  • Shorter hospital stays,
  • Reduced hospital-associated costs,
  • Faster return to normal activity,
  • Improved clinical outcomes,
  • Improved scar appearance, and
  • Greater patient satisfaction

Ideally, when a new or modified surgical technique is developed, other variables are controlled; the only thing that is being tested is the technique. As MISTHA was being developed, there arose the opportunity to change anesthesia protocols; due to the more limited surgical exposure and the reduced soft tissue damage, MISTHA could be performed with sedation and spinal anesthesia instead of general anesthesia. For the same reasons, it was also possible to improve the pain medication protocol. Because MISTHA patients do not have to overcome the lingering side effects of general anesthesia (dizziness, nausea, and headaches), and because they have less postoperative pain, rehabilitation can begin more quickly and therefore the return to normal functional activities is faster.

Protocol Changes

  • Anesthesia – sedation & spinal anesthesia
  • Pain medication
  • Quicker rehabilitation initiation

The changes in these protocols make it more difficult to clearly evaluate the direct influence of incision size, soft tissue disruption, and reduced blood loss on recovery and return to normal activities. It is unclear if the protocol changes alone could have caused the beneficial effects regardless of surgical procedure.

What are the possible problems with MISTHA?

A major reservation about MISTHA is the success of conventional THA. Decades of data and experience have shown that conventional THA offers excellent long-term outcomes such as: pain relief, return to function, durability, and low complication rates. Skeptics are concerned that MISTHA will fail to meet expectations, will compromise the benefits of conventional THA, and will introduce new problems due to the reduced visual field. Concerns include malpositioned implants, neurovascular injury, poor implant fixation, and compromised long-term results.

Possible Problems

  • Malpositioned implants
  • Neurovascular injury
  • Poor implant fixation
  • Compromised long-term results

What does recent research tell us?

In reports of two-incision MISTHA outcomes, excellent results were obtained for all patients.[i],[ii] When an outpatient protocol was applied[ii], 85% of patients went home on the day of surgery and all patients had been discharged to home within 23 hours. All patients had resumed normal daily activity within 10 days postoperative. This protocol includes an accelerated rehabilitation plan, non-general anesthesia, and a new pain management scheme (discussed above). There were no readmissions, no dislocations, and no reoperations. Both the two-incision MISTHA and the outpatient protocol were deemed safe and effective. More recently, at AAOS 2005, clinical results from the two-incision MISTHA were very encouraging: no complications and early rehabilitation for patients.[iii] Two other studies of complication rates with two-incision MISTHA were less favorable.[iv],[v] In one of these studies, 80% of patients were discharged directly to home in two to three days postoperative and 14% of all patients experienced substantial complications.[vi] In the second study, 10% of patients required reoperation within six months of two-incision MISTHA.[v] A single study on the importance of cosmesis and patient priorities for the two-incision MISTHA was also presented at AAOS 2005.[vi] Patients with two-incision MISTHA were compared to patients with conventional THA at a minimum of one-year postoperative via direct mail questionnaire. At least 95% of responding patients in both groups reported that their scars looked good, but the MISTHA group had significantly higher incidence of sunken or curled scar edges (p = 0.001). More interesting than the appearance of scarring, was the priorities reported by patients. Of highest priority was regaining normal activity, avoiding infection, and decreasing hip pain. Least important was cosmetic appearance, length of hospital stay, surgical costs, and time away from work.

Two-incision MISTHA

  • “excellent results (especially with changed protocols) & no complications” vs.
    “increased complications”
  • “95% of patients believe their scars look good, regardless of incision length” vs.
    “cosmetic appearance of scar is of little importance to patients”

MISTHA single-incision studies include: blood loss for MISTHA compared to standard THA,[vii] and overall outcome studies.[viii],[ix],[x],[xi] None of these studies reported a significant difference for single-incision MISTHA compared to standard THA for any of the measured parameters: intraoperative blood loss, length of surgery, length of hospital stay, patients’ disposition after discharge, narcotic usage, rehabilitation, return to function, or complications.

Single-incision MISTHA (no significance difference compared to standard THA)

  • Intraoperative blood loss
  • Length of surgery
  • Length of hospital stay
  • Discharge disposition
  • Narcotic usage
  • Return to function
  • Complication rate

Summary

In summary, data and experience will address whether the predicted benefits of MISTHA are met. Choosing MISTHA or conventional THA will most likely be a matter of surgeon experience and skill, and patient physical condition.

Points to Remember

  • There is no standard definition for minimally-invasive total hip arthroplasty and since there are numerous THA procedures using shorter incisions, no single definition is available; only a need to be more specific when discussing those procedures.
  • The goals and benefits of MISTHA are achievable in certain circumstances, but should not be assumed to have been achieved for all MISTHA procedures.
  • As MISTHA continues to evolve, there is a continued need for evolution in the design and functionality of instrumentation and components.

Copyright (c) 2005                Susan G. Capps, Ph.D.


[i] Berger RA: Total hip arthroplasty using the minimally invasive two-incision approach. CORR 417:232-241, 2003.

[ii] Berger RA et al: Rapid rehabilitation and recovery with minimally invasive total hip arthroplasty. CORR 429:239-247, 2004.

[iii] Yoon TR et al: Minimally invasive total hip arthroplasty: Comparison between one-incision and two-incision technique.

Paper No. 147, AAOS 2005.

[iv] Pagano MW et al: Two-incision total hip arthroplasty in 80 consecutive unselected patients: Prevalence of complications.

Paper No. 144, AAOS 2005.

[v] Ball BS and Haltrom Jr JD: Complications associated with the two-incision technique in primary total hip arthroplasty.

Paper No. 143, AAOS 2005.

[vi] Goldstein WM et al: Patient priorities and importance of cosmesis after total hip arthroplasty: Standard versus minimal incision. Paper No. 138, AAOS 2005.

[vii] Earles DR and Pierson JL: Minimally invasive total hip arthroplasty does not reduce blood loss compared to standard technique. Poster No. P006, AAOS 2005.

[viii] Woolson ST et al: Comparison of primary total hip replacements performed with a standard incision or a mini-incision. JBJS 86A(7):1353-1358, 2004.

[ix] Mahoney OM et al: The effect of incision size on clinical outcomes and recovery after total hip arthroplasty with the antero-lateral approach. Paper No. 208, AAOS 2004.

[x] Ogonda L et al: A minimal-incision technique in total hip arthroplasty does not improve early postoperative outcomes. A prospective, randomized, controlled trial. JBJS 87A(4):701-710, 2005.

[xi] Rothman RH et al: Total hip arthroplasty: Does incision length matter. Paper No. 137, AAOS 2005.

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