The Effect of Infrapatellar Fat Pad Resection in Total Knee Replacement on Patella Tendon Length and Functional Outcomes after Five Years

Introduction

The infrapatellar fat pad (IPFP) is an extrasynovial structure consisting of fibrous adipose tissue and is situated in the anterior compartment of the knee joint, between the joint capsule and the synovium. The IPFP may be entirely or partially excised during total knee replacement (TKR) to facilitate the surgeon’s view of the lateral tibial plateau. Joint Registry data from the United Kingdom (UK) showed that 27% of surgeons excise the IPFP in its entirety, 59% partially resect it, and 14% leave the IPFP intact [1].

It remains unclear whether IPFP excision leads to patella tendon shortening. Patellar tendon shortening is known to occur after surgery on the knee [2, 3, 4, 5, 6, 7, 8]. Shortening of the tendon alters the biomechanics of the knee and can be problematic. It is directly related to anterior knee pain and decreased range of motion after TKR [5]. It can cause patella impingement on the tibia in full flexion. Patella infera is a cause of patellofemoral pain, stiffness, and reduced functional scores after knee replacement [9].

The pathophysiology of postoperative patellar tendon shortening is believed to be multifactorial [10]. It may be due to intrinsic collagen contraction, scarring and contraction of peripatellar soft tissues, ischemic contracture of the tendon, or quadriceps weakness from prolonged knee immobilization or pain inhibition [10, 11]. It has been shown that complete IPFP excision can devascularise the patella by interrupting the infrapatellar anastomosis [12, 13]. This same anastomosis supplies the patella tendon.

The clinical outcome of TKR is dependent on numerous factors including patient selection, prosthesis design, surgical technique and rehabilitation programs. The surgical technique and subsequent tissue handling probably influence prospective rehabilitation and symptoms. Resection of IPFP during TKR may have short and long-term effects on clinical outcomes [14, 15, 16, 17, 18, 19].

Recent systematic review articles have highlighted the paucity of data on the effect of IPFP resection on patient satisfaction scores [19, 20]. Only one retrospective study was identified, which looked at 8231 TKRs in the UK and found no significant difference in patient satisfaction across three groups of patients who had either complete resection, partial resection or preserved IPFP [21].

To our knowledge, there are no evidence-based consensus guidelines on whether to respect the IPFP during TKR.

Aim and Methods

Our aim was to compare patellar tendon length and functional outcome scores after knee arthroplasty for osteoarthritis, between patients in whom the infrapatellar fat pad was completely excised and those in whom it was preserved.

We conducted a retrospective study looking at resection versus preservation of the infrapatellar fat pad in primary total knee replacements. Consecutive cases were identified via the Joint Replacement Arthroplasty Clinic (JRAC) Database at Royal Perth Hospital between 2007-2009 using the Stryker Triathlon or Duracon implants between two independent consultant surgeons.

Sample size calculations based on the study by Meneghini, et al. [14] estimated 54 patients in each group to have an 80% chance of detecting a 5% difference in change of length of the patellar tendon between the groups at a 5% level of significance. Patients with primary osteoarthritis aged 18 years or older were included in this study. The exclusion criteria were inadequate radiographs, previous knee surgery (High Tibial Osteotomy, ACL reconstruction, etc.), inflammatory arthropathy, postoperative sepsis, intraoperative tibial plateau fractures, bilateral total knee replacement and intraoperative lateral release.

168 consecutive records were reviewed (77 resection vs 91 preserved) with true lateral xray taken at 30 degrees of flexion. Imaging was taken preoperatively, 1yr post operatively and 5yrs post operatively and reviewed by three independent clinicians blinded with the mean patella tendon ratio recorded. Functional measures were recorded by independent musculoskeletal physiotherapists through the JRAC program.

Results

168 consecutive patients were retrospectively recruited into this study. Baseline demographics were similar between resection and preservation groups with a mean age of 68.5 (70 vs 67, p=0.17), BMI 31.71 (31.02 vs 32.4, p=0.84) and patella resurfacing 23.5 (24 vs 23, p=0.29).

1 A comparison was made between the resection and preservation groups for the Insall-Salvati ratio preoperatively (0.98 vs 0.99, p=0.77), at one year postoperatively (0.97 vs 0.97, p=0.87) and five years postoperatively (0.91 vs 0.92, p=0.75).No statistical difference was found at any time period (Figure 1).

at one year postoperatively (1.36 vs 1.40, p=0.15) and five years postoperatively (1.30 vs 1.34, p=0.23) (Figure 2).

1.6

Whilst statistically significant differences were detected with the Blackburne-peel ratio at one year post operatively (0.82 vs 0.77, p=0.034) and five years postoperatively (see figure 3) for the Catondeschamps

0.85 ratio (0.77 vs 0.84, p=0.012) (see figure 4) these may not be clinically significant given that these measures are dependent on where the tibia is resected.

0.9

statistical significance between groups preoperatively (50.6 vs 42.8, p=0.3) and at five years post operatively (69.4 vs 62.0, p=0.88).

0 10 20 30 40 50 60 70 80 90 100

80

Discussion

It remains unclear from the literature as to whether IPFP resection contributes to patella tendon shortening. Macule, et al. [14] conducted a randomized controlled trial assessing patellar tendon length at 5 days, 1 and 6 months postoperatively across two groups; one in which IPFP was excised and one in which it was preserved. Macule, et al. [14] found no significant difference in patellar tendon length between the two groups (p>0.05) [14]. Pinsornsak, et al. [15] made the same observation in their randomized controlled trial in patients up to 12 months follow-up [15].

Lemon et al had a longer follow-up period of 1-3years post TKR. They observed a statistically significant shortening of the patella tendon (p=0.004) in the group that had the IPFP resected [16]. Tanaka, et al. [7] observed statistically significant shortening of the patella tendon at 28– 38months post TKR in the IPFP resection group (6.6mm shortening, p<0.05), whilst the IPFP preservation group did not have significant tendon shortening (3.9mm, p>0.05) [7]. Gwyn, et al. [17] found complete excision of the fat pad had a significant shortening effect on the tendon in their retrospective radiological study [17]. However, Meneghini, et al. [18] had conflicting findings in their large retrospective study (n=1055). They found no significant difference in patellar tendon length at 5.1 years post-TKA whether the IPFP was preserved or resected [18].

The literature is divided on the effect of IPFP resection on anterior knee pain. Pinsornsak, et al. [15] found after a minimum of 6-months post-op there was a significantly higher incidence of anterior knee pain in TKRs where the IPFP was resected compared to when it was preserved [15]. Meneghini, et al. [18] made the same observation at 5.1 years follow-up [18]. Tanaka, et al. [7] also found a higher incidence of anterior knee pain in the resected group [7]. Conversely, Macule, et al. [14] observed higher rates of anterior knee pain amongst the preservation group at 6-months post op [14].

Similarly, there have been mixed findings on the effect of excising the IPFP on post-operative range of motion (ROM) in TKRs. At 1 year, Pinsornsak, et al. [15] found no difference in knee ROM between TKRs that had the IPFP resected and those in which the IPFP was preserved. Tanaka showed a statistically significant decreased ROM in the resection group at both 1-2 months and 28-38 months (both p<0.05) [7]. However, at 5.1-year follow-up, Meneghini, et al. observed no difference in ROM between the two groups [18].

This study demonstrates no significant difference in tendon length or functional outcome scores between resection and preservation of the infrapatellar fat pad in the setting of primary total knee replacement. The strengths of the study are that it was conducted at a single institution using a single implant in consecutive patients. Findings are somewhat limited given it is a retrospective study and does not take into account variations in patient comorbidities. Future prospective trials may be of benefit in confirming the results of this study and it may also be useful to compare other functional outcome scores such as the oxford knee score which has a component to address the effect of kneeling after arthroplasty surgery.

Conclusion

There is no statistical difference in radiological measures or functional scores (AKPS &KSS) at one or five years post-operatively between groups having resection or preservation of the infrapatellar fat pad following total knee arthroplasty for primary osteoarthritis [22, 23, 24, 25].