Minimally Invasive Computer-assisted Total Knee Arthroplasty Through a Subvastus Approach

Abstract

Computer-assisted total knee arthroplasty (TKA) has traditionally been performed through an anterior midline incision approximately 16 cm long, using a capsular incision that separates the interval between the rectus femoris and vastus medialis muscles. The incision disrupts the suprapatellar pouch and frequently leads to adhesions and difficulty in fast and complete flexion recovery despite the wide exposure. The minimally invasive surgery subvastus approach with computer-assisted soft tissue balancing using OrthoPilot TKA (B. Braun Aesculap, Tuttlingen, Germany) not only provides optimal alignment and balancing of the components but also results in maximal and faster flexion recovery and reduces the need for postoperative narcotic medication.

This retrospective study compared 26 computer-assisted total knee arthroplasties (TKAs) (e.motion, B. Braun Aesculap, Tuttlingen, Germany) performed using a minimally invasive surgery (MIS) subvastus approach (with 26 computer-assisted TKAs (e.motion) performed using a mini-standard medial parapatellar approach. Preoperative clinical and radiography Knee Society scores as well as postoperative functional outcomes were compared.^1,2

The tourniquet time and amount of closed-suction blood drainage were recorded to estimate blood loss. Postoperative flexion was measured daily during hospitalization, with follow-up measurements at 6 weeks, 3 months, and 6 months postoperatively. Pain levels were assessed using a visual analog scale and by the amount of pain-control drugs administered during hospitalization. Implant alignment was measured through long radiography films in standing position and in standard anteroposterior and lateral projections.

Results

The average skin incision was 9 cm long for the minimally invasive surgery (MIS) group compared with 14 cm for the standard approach group. Tourniquet time was 52 minutes in the standard group versus 61 minutes in the MIS group. The significantly longer time for the MIS group (9 minutes) was attributable to the extra time required for the flexion/extension knee position change during surgical steps for joint exposure and for inserting a retractor, which is difficult without patellar eversion.

No significant difference was recorded in the estimated total blood loss through drainage: 730 mL (SD±65 mL) for the standard group versus 780 mL (SD±255 mL) for the MIS group. The lack of significant difference is probably attributable to the fact that rod invasion for medullary canal alignment is avoided in the computer-assisted surgery technique in both approaches.

Pain reduction was a significant benefit of the MIS approach. In addition to the narcotic pain medication administered through the epidural catheter (naropine, 2 mg/mL at 5 mL/h in elastomeric pump for 60 hours), the total dose of subcutaneously administered narcotic pain medication was standardized to morphine sulfate equivalents (Eptadone) in milligrams and recorded daily. The daily dose of morphine sulfate equivalents was significantly lower in the MIS group postoperatively on days 0 and 1 and extremely lower on postoperative days 2 and 3, at which point the epidural catheter was disconnected. The total dose of morphine sulfate equivalent used by the standard group was 113 mg (SD=120 mg) versus the MIS group with 23 mg (SD=35 mg), yielding P=.01.

table

Flexion in the MIS group was significantly stronger at postoperative day 5 (105/MIS group versus 88/Standard group). Active and passive flexion was recorded daily for 1 week; the results were significantly better in the MIS group. At the 6-week postoperative follow-up, the average passive flexion was 132° for the MIS group and 122° for the standard group, with more difference between the groups at 2 weeks and less difference at 3 and 6 months (Table).

In radiograph alignment evaluation in anteroposteror and lateral projections, no difference was observed between the MIS approach and the traditional approach. Component positioning was sufficient in both groups (Figure). Equally excellent stability for varus and valgus and anteroposteror stresses were found in both groups, with no significant difference observed between them. Significant differences over time and between groups were observed for both scores from the first evaluation period (P<.001).

There was 1 patient with distal deep vein thrombosis in the MIS group, compared with 2 patients in the standard group, which included 1 patient with hematoma and 1 patient with arthrofibrosis with severe rigidity. These patients were treated with arthroscopic arthrolysis 7 months’ postoperatively.

Figure: Equally excellent stability for varus and valgus and AP stresses were found in both groups, with no significant difference between them.

Discussion

During the past 30 years, several surgical approaches have been used for TKA. Difficulties in regaining motion and suprapatellar adhesions caused arduous and often painful recuperation periods. “Minimally invasive” is a general term to describe procedures performed through smaller incisions with maximum deep tissue protection. The primary advantage of a minimally invasive TKA procedure is the less invasive treatment of quadricep muscles and deep tissue. A secondary benefit is the smaller skin incision.^3-6

When the knee was extended, the soft tissue window moved proximally; when the knee was flexed, the soft tissue window moved distally. A standard posterior cruciate ligament (PCL) retractor held the patella laterally displaced, but not everted. This reduced the tension on the patellar tendon, which reduced the risk of avulsion or damage. Obesity is not a contraindication to using this incision, although it should not be attempted in morbidly obese patients. In heavily muscled patients, the incision may be inadequate because it will be extremely difficult to displace the quadriceps system and the patella laterally.

The tourniquet remained inflated for an average of 9 minutes longer in the MIS group compared with the standard group. The increase may reflect the extra time required to change knee positions during surgery and to install retractors. A less invasive surgical approach was thought to increase blood loss postoperatively. In fact, patients in the MIS group showed a slight trend toward increased output. The effect is not significant, however, and is accompanied by faster flexion recovery. Faster flexion recovery may be the reason for the slight increase in wound drainage in the MIS group.

Pain reduction is the greatest benefit of the MIS approach. Visual analog scores as well as the required amounts of narcotic medication administered through the epidural catheter were significantly lower for the MIS patients than for the standard patients. The pain relief advantage persisted after the epidural catheter was removed. The MIS group needed significantly less morphine sulphate (P=.008), in equivalents of oral medication, than the standard group. A second beneficial effect of the minimally invasive approach is related to the rate of flexion recovery after surgery. More than 85% of the patients in the MIS group achieved more than 90% flexion by postoperative day 2, whereas in the standard group, this degree of flexion was usually not obtained until postoperative day 5. The MIS group continued to show a more rapid return of flexion, which allowed discharge of MIS patients from the hospital approximately 30% earlier than the patients treated through the standard approach. Furthermore, the patients in the MIS group showed a wider flexion range than the patients in the standard group at the 45-day and 60-day postoperative evaluations. Only at 3 months did the results for passive flexion appear to converge for the two groups.

Finally, no significant difference was found regarding component alignment. Ligament balancing was equally excellent in both groups, with no significant difference observed between the two groups.^7-9 This result can be attributed to additional essential improvements implemented in the latest release of the OrthoPilot TKA software, which was used for both groups in this study.

Conclusion

The advantages expected of the minimally invasive technique, including reduced postoperative pain, increased range of motion, smaller incision, faster recovery times, shorter hospital stays, shorter (generally by 2 months) postoperative physical rehabilitation periods, and reduced blood loss, could be confirmed by the statistical comparison of two similar groups of young and mobile patients. The results of this short-term study show a clear trend, which should be confirmed by a longer-term evaluation.

Minimally invasive quadriceps-preserving, computer-assisted TKA can be recommended for most patterns of knee osteoarthritis, not only to ensure the best possible functional results but also to achieve the longest possible durability of the prosthesis, which is closely correlated to optimal component alignment and ligament balancing, especially for highly demanding and mobile young patients.

References

Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res. 1989; 248:9-12.
Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res. 1989; 248:13-14.
Hofmann AA, Plaster RL, Murdock LE. Subvastus (Southern) approach for primary total knee arthroplasty. Clin Orthop Relat Res. 1991; 269:70-77.
Goble EM, Justin DF. Minimally invasive total knee replacement: principles and technique. Orthop Clin North Am. 2004; 35:235-245.
Tria AJ Jr, Coon TM. Minimal incision total knee arthroplasty: early experience. Clin Orthop Relat Res. 2003; 416:185-190.
Tria AJ Jr. Advancements in minimally invasive total knee arthroplasty. Orthopedics. 2003; 26:S859-S863.
Clemens U, Miehlke RK. Experience using the latest OrthoPilot TKA software: a comparative study. Surg Technol Int. 2003; 11:265-273.
Saragaglia D, Picard F, Chaussard C, et al. Computer-assisted knee arthroplasty: comparison with a conventional procedure. Results of 50 cases in a prospective randomized study. Rev Chir Orthop Reparatrice Appar Mot. 2001; 87:18-28.
Sparmann M, Wolke B, Czupalla H, et al. Positioning of TKA with and without navigation support. A prospective randomised study. J Bone Joint Surg Br. 2003; 85:830-835.

Author

Dr Zanasi is from the Villa Erbosa Hospital, Bologna, Italy.