Background
In addition to conventional surgical approaches, total knee arthroplasty (TKA) may be done by means of minimally invasive surgery (MIS). Minimally invasive TKA (MIS-TKA) is often portrayed in the lay community and press as involving a small skin incision. Actually, MIS-TKA is defined by limited soft-tissue and bony dissection. MIS-TKA was developed after the description of unicondylar knee arthroplasty. [1, 2]
Conventional TKA is a successful operation for patients suffering from arthritis of the knee, with a reported complication rate of less than 2% and an implant survivorship of 95% at 10 years. The aim of MIS-TKA is to decrease postoperative pain and shorten the rehabilitation period.
Indications
MIS-TKA is used as an alternative to conventional TKA. However, there are conflicting data on whether MIS-TKA is an acceptable replacement for or even an improvement on conventional TKA, and no definitive answer to this question is available at present.
Contraindications
No absolute contraindications exist for MIS-TKA; this procedure is defined by limited soft-tissue and bony dissection. Conventional TKA is probably a more suitable choice for the following patients [3, 4, 5] :
-
Patients with a body mass index (BMI) greater than 40 kg/m 2
-
Patients with severe fixed valgus deformity
-
Patients with severe osteoporosis
-
Patients who have previously undergone knee arthrotomy
-
Patients with rheumatoid arthritis
Technical Considerations
Complication prevention measures recommended for MIS-TKA are exactly the same as those recommended for conventional TKA and should include the following:
-
Appropriate preoperative screening and clearance
-
Preoperative templating and planning
-
Preoperative administration of antibiotics as recommended by the American Academy of Orthopaedic Surgeons (AAOS)
Outcomes
Early series comparing MIS-TKA with conventional TKA reported successful outcomes. [6, 7] A meta-analysis of 38 studies (9296 TKAs) reported shorter hospitalization times and shorter times to complete an active straight-leg raise with MIS-TKA than with conventional TKA. [8] A retrospective review of 48 knees found that MIS-TKA patients could complete an active straight-leg raise earlier than conventional TKA patients could. [9] A study comparing computer-assisted approaches reached a similar conclusion. [10] A case-control study comparing conventional TKA and MIS-TKA in 32 knees cited mean Knee Society Scores (KSS) of 94 and 96 and mean functional scores of 90 and 99, respectively. [11]
A randomized controlled trial (RCT) that investigated extensor and flexor muscle function after conventional TKA and after MIS-TKA found that the MIS-TKA group had a higher knee extensor peak torque at 3, 6, and 12 months postoperatively. [12] Similarly, another RCT found that the MIS-TKA group had greater hamstring and quadriceps strength at 4 weeks after surgery; however, this difference was not observed at 12 weeks, and no benefit was documented with regard to longer-term strength or functional performance. [13]
Another prospective RCT, which compared conventional TKA with MIS-TKA by using an accelerometer, found that MIS-TKA patients were significantly more active on all postoperative days and that MIS-TKA patients achieved 80% of their preoperative acceleration in about half of the time that conventional TKA patients took to reach this level. [14]
Additionally, a systematic review of 13 randomized controlled trials found that the mean KSS at 6 and 12 weeks postoperatively was higher in the MIS-TKA group but that this difference was lost at 6 months. [15] Finally, a long-term cohort study of a group of 192 patients determined that there was a 95% 10-year implant survival rate, with excellent functionality and clinical outcomes according to the Oxford Knee Score (OKS). [16]
Conflicting conclusions demonstrate why there is still no consensus regarding either the noninferiority or the superiority of MIS-TKA as compared with conventional TKA. A prospective RCT found that as expected, incisions were significantly shorter in the MIS-TKA group, but there were no significant differences in the Knee Injury and Osteoarthritis Outcome Score (KOOS), the OKS, the KSS, and the Short Form (SF)-12 score at 6-week, 1-year, 2-year, and 5-year follow-up evaluations in comparison with conventional TKA. [17]
A meta-analysis of 30 RCTs (2500 TKAs) examined short- to midterm results (< 36 months) for MIS-TKA as compared with conventional TKA. [18] The authors concluded that the MIS-TKA group had better outcomes with respect to KSS, range of motion (ROM), days to straight leg-raise, and total blood loss. However, this benefit was associated with longer operating and tourniquet times, as well as wound-healing complications. Overall, though, there were no significant differences between MIS-TKA and conventional TKA with regard to radiographic evaluation of component positioning.
A subsequent meta-analysis of 11 trials (1025 TKAs) confirmed these findings. [19] The authors concluded that the MIS-TKA approached was an effective and safe alternative to conventional TKA.
An RCT that evaluated medium-term results demonstrated that at a mean of 6 years' follow-up, there were no differences between MIS-TKA and conventional TKA in terms of pain, function, malalignment, or revision rates. [20]
A retrospective study that included 74 TKAs documented a good survival rate (94.7%) for MIS-TKA using implants specifically designed for MIS at a minimum follow-up of 10 years (range, 10-12.8 years), with no cases of prosthesis-related revision. [21] Good clinical and radiographic outcomes were achieved.
-
Minimally invasive total knee arthroplasty (MIS-TKA). Midline skin incision is performed. Mini-incision is approximately twice length of patella, 6-14 cm (blue); conventional incision is longer (red extensions).
-
Minimally invasive total knee arthroplasty (MIS-TKA). Parapatellar (ie, medial parapatellar, midvastus, subvastus, or lateral) arthrotomy is performed to access knee joint and perform arthroplasty.
