Introduction

It is hard to summarize surgical pearls since this text is dedicated to pearls and techniques for successful partial knee arthroplasty. Many of these pearls may be discussed elsewhere by experienced authors and surgeons, but I will elaborate on pearls that I believe help facilitate the unicompartmental procedure for fixed-bearing designs. While much of this information is discussed and expanded elsewhere, this chapter should serve as a summary of surgical tips and pearls to improve these outcomes, not only patient outcomes, but may translate into making the procedure a bit easier for the surgeon.

Skin Incision

The first pearl is regarding the skin incision. In the early 1990s, a resurgence in unicompartmental arthroplasty occurred largely due to the newer minimally invasive surgery (MIS) techniques introduced. Certainly, the size of the incision should be directly proportional to the experience of the operating surgeon. Under no circumstances should a small incision be used that results in a surgical compromise. The incision must be large enough to allow for adequate visualization so proper bone cuts can be made, flexion and extension gaps are balanced, other compartments may be visually inspected and anterior cruciate ligament (ACL) integrity evaluated, and proper femoral and tibial sizing can occur without overhang or impingement.

The ACL can be visualized at the time of the arthrotomy, but visualization of an intact ACL is not always required. Certainly more important appears to be the stability of the knee. An examination under anesthesia can be performed and stability of the ACL assessed. A nonfunctioning ACL with an unstable knee increases the sliding forces that can eventually lead to early polyethylene wear and joint failure. Engh and Ammeen reported on the results of unicompartmental knee arthroplasty without an intact ACL, and good results can be obtained if functional instability is not present.¹ This differs from the classic article by Goodfellow and O’Connor that showed a higher failure rate without an intact ACL. Therefore, the emphasis is on knee stability, not ACL integrity.² Visualization at the ACL does not answer completely the status of the ACL. Cushner et al. not only described significant loss of the ACL at the time of indicated total knee arthroplasty, but pathologic changes in the “viable” ACL were also noted.³ Mullaji et al. recently evaluated tibial cartilage wear in patients undergoing total knee arthroplasty and found that the articular wear pattern can provide clues to the functional status of the ACL.⁴ Posterior-half involvement of the medial plateau was more commonly seen when a functional ACL was not present. This is a helpful pearl since studies from Trompeter et al. showed that the clinical appearance of the ACL was not a good predictor of severity on microscopic examination.⁵

Certainly, the size of the incision should not compromise results. Hamilton et al. reviewed 221 unicompartmental arthroplasties performed using the MIS technique.⁶ This cohort was compared to a cohort of 514 standard-incision unicompartmental knee arthroplasty patients. In the MIS group, 9 of 221 were revised for loosening. Of the remaining 212 patients, 16 patients required 18 nonrevision reoperations. In other words, 25 of 221 required at least one reoperation (11.3%). This compared to 8.6% for the standard-incision group, with a higher aseptic loosening rate also noted in the MIS group (3.7% vs. 1%).

Decreasing Blood Loss

Once a skin incision is made, a surgical pearl to decrease blood loss is to inject the knee arthrotomy site with a lidocaine (Marcaine)/epinephrine solution. Thirty milliliters injected along the arthrotomy site did result in a significant decrease in blood loss in our total knee arthroplasty patients.⁷ While this procedure was initially described in a total knee arthroplasty patient, it could be also performed in unicompartmental arthroplasty patients. We have extended the use of lidocaine with epinephrine to all arthrotomy patients with the goal of not only less bleeding and fewer transfusions but overall less hematoma in the joint postoperatively. Our thoughts are that less blood in the joint improves the patient’s function. Periarticular steroid injections can also be used to improve outcomes following unicondylar knee replacement. Pang et al. recently performed a prospective randomized study comparing 90 knees over a 2-year period where injection with triamcinolone acetonide, bupivacaine, and epinephrine was compared to a control group in which only bupivacaine and epinephrine injections were performed. Improvement was noted in midterm and short-term results with no increase in infection or tendon failures reported.⁸

Solid Repair of the Arthrotomy

Another pearl utilized at our institution is a solid repair of the arthrotomy. If a solid repair is not performed, this can result in late patella instability and subluxation. We believe that a more watertight seal can not only improve knee appearance but also result in less wound drainage in the immediate postoperative period. We currently utilize a bidirectional barbed suture design to facilitate arthrotomy closure (Quill Suture; Angiotec, Vancouver, British Columbia). Our initial studies showed that not only did we achieve a shorter operating time secondary to a quicker closure of the arthrotomy, but a more watertight closure was also described in the laboratory setting^9,10 (Fig. 9–1).

Figure 9–1 Use of a barbed suture (Quill Suture; Angiotech, Vancouver, British Columbia) to aid in watertight closure.

Tibial Bone Cuts

There are numerous pearls when it comes to completing the tibial bone cuts. As with all knee procedures, the accuracy of the tibial cut must be stressed. In several ways, a tibial cut for unicompartmental knee is a bit more difficult since mis-cuts or malaligned cuts can be less forgiving during the postoperative period. For example, Hernigou and Deschamps demonstrated that extreme tibial slope could increase failure rates and concluded that a slope of greater than 7° should be avoided.¹¹ A pearl to avoid excessive slope is to use an angel wing or similar type of device and place it in the cutting guide before the osteotomy is performed. The amount of bone resected anteriorly should be similar to that resected posteriorly (Fig. 9–2). If this occurs, then the slope is well within the 7° limit. The depth of the resection also needs to be precise to avoid the complication of a posterior plateau fracture. These fractures are multifactorial and certainly can be minimized with a more conservative initial cut (2–3 mm), with the ability to cut more bone if needed.

Figure 9–2 Tibial fragment assessed for proper slope.

Limiting of guide fixation pins may also play a role, because the more pins utilized, the higher the risk of fracture. Seon et al. reported two occasions of shear fracture as a result of number of guide pins utilized.¹² Yang et al. showed similar results that appear to be associated with the technique related to the tibial osteotomy guide.¹³ Van Loon et al. reviewed peripheral tibial plateau fractures and, once again, they appeared to be related to surgical technique. This complication can be avoided by limiting the number of fixation pins, achieving the proper cutting depth, exercising caution when utilizing the operative mallet, and ensuring proper component sizing.¹⁴ Brumby et al. evaluated tibial stress fractures and noted that the use of three or more fixation pins did increase their occurrence.¹⁵ They felt that, if three or more pins were deemed necessary, the risk of stress fracture increases. Peripheral pins must not violate the medial cortex and should be avoided if at all possible.

One means to avoid damage to the anterior cortex of the tibia is using caution on removing the osteotomy fragment. We like to remove it in one piece because the osteotomy fragment can serve as a good template for the proper-size tibial component (Fig. 9–3). To remove it in one piece without damage to the anterior cortex, we often use a tibial guide and place an ostium on leveling off the tibial guide, not the anterior cortex. By pushing up from the anterior guide and pulling the tibial fragment forward, the piece can be removed intact to be used for sizing purposes and the anterior rim of the cortex is not damaged (Fig. 9–4).

Figure 9–3 (A) Removing the tibial bone fragment whole for examination. (B) Use of the fragment as a template for tibial sizing.

Figure 9–4 Use of an osteotome to wedge the tibial fragment without causing damage to the anterior tibial cortex.

Sagittal saw extension can be another source of error resulting in a reduction of the loading capacity of the tibia. When performing these cuts, the vertical cut should not penetrate greater than the total depth that is to be removed. Leaving in the same blade helps protect against undercutting the ACL insertion area.

Simpson et al. evaluated bone strain and found that a 40% increase is noted after implantation.¹⁶ This increased stress reaction may be what contributes to the vague medial pain often seen in the initial 12 months following the unicompartmental procedure. Proper patient assurance is required if no fracture is found but medial pain exists. Unusually by the 12-month mark, these symptoms resolve as bone remodeling occurs.

Cement Technique

Other surgical technical pearls to avoid complication are related to the cement technique. Retained cement leaves the surgeon with an unacceptable postoperative radiograph and may cause pain for the patient, requiring reoperation for removal of the retained cement. As with most things, prevention is the best treatment. This may involve the placement of a gauze posteriorly to allow for protection should posterior protrusion occur. The cement technique also can decrease the occurrence of retained cement. We like to wash, dry, and actually impact the cement off the plateau to allow for better bone penetration. Less cement is placed more posteriorly to help avoid protrusion, and the components are inserted in a posterior-to-anterior fashion to try to extrude the cement anteriorly around the posterior origin, where it is more difficult to see. Proper tools are also needed, such as curettes to remove any retained cement. In difficult cases an arthroscope can be placed and retained cement can be removed under direct visualization, but we find that with proper technique this is not often required.

Inserting the prosthetic component when the cement is in a less liquid form allows for easier removal of retained cement, although this is a bit of a gamble since no one wants the cement to harden before proper positioning has been achieved. To prevent loosening, more than proper cementing is required for a good cement-prosthesis interface. We have talked about pressurization of the bone cancellous surface but a cancellous surface needs to be prepped before the cement technique is performed. This includes washing as well as drying the tibial surface. Sclerotic bone can be drilled to allow better cement penetration and enhance tibial fixation. In all cases, cementing should include drilling, washing, drying, and then modern cement techniques as described with all retained cement removed.

Femoral Component

In regard to the femoral component, proper sizing is critical, and impingement needs to be avoided. Numerous systems allow for a linkage of the tibial cut to the femoral cut. The advantage here is that no intramedullary hole is placed, hence eliminating the blood loss that occurs from the intramedullary hole. The difficulty often encountered with the link system is that the distal cut is made in the extended position. One pearl is that the cut can be initiated in the extended position but completed with a flexed knee, which is more within most surgeons’ comfort zones.

Conclusion

In closing, there are many ways in which unicompartmental arthroplasty provides long-term successful results. The above pearls and technical suggestions may help make the procedure a bit easier as well as help to avoid commonly seen complications.