The Journal of Arthroplasty Vol. 24 No. 4 2009

Scintigraphic Assessment of Patellar Viability inTotal Knee Arthroplasty After Lateral Release

Uday Pawar, Diploma Ortho, DNB Ortho,* K. Narasimha Rao, MS Ortho,*P. Shanamuga Sundaram, DRM Nuclear Medicine,†

Jai Thilak, MSMcH, Ortho,* and Jacob Varghese, MSMcH, Ortho*

Abstract: To what extent lateral retinacular release done in total knee arthroplastycompromises patellar viability has been debated. This study is a prospective study toassess patellar viability using Technetium-99mmethylene diphosphate (Tc-99mMDP)scintigraphy. Between 2005 and 2006, 59 patients (72 knees) who underwent primarytotal knee arthroplasty were studied, of which 36 required lateral release. All patientsunderwent regional bone scan using Tc-99m MDP before and 1 to 3 weeks afterthe surgery. Two nuclear medicine consultants using both qualitative andquantitative assessment interpreted the scans independently. Fourteen knees withlateral release showed scintigraphic signs of hypovascularity in the early post-operative period that normalized in 8-week postoperative period. This studydocuments the greater incidence of transient patellar hypovascularity associatedwith lateral release. Key words: lateral release, total knee arthroplasty, transient,patella, scintigraphy.© 2009 Elsevier Inc. All rights reserved.

Lateral release in total knee arthroplasty is done toenable proper patellofemoral tracking and as a partof the lateral approach in a valgus knee. Inconventional medial parapatellar approach with alateral release, all the peri patellar feeders except forthe recurrent branch of anterior tibial artery will becompromised. The association of hypovascularityand lateral release has been demonstrated andvaries from 10% to 56% [1,2]. There have beencontradicting reports that lateral release could resultin osteonecrosis and patellar fracture. There has

From the *Department of Orthopaedics, Amrita Institute of Medicalsciences, Kochi, Kerala, India; and †Department of Nuclear medicine,Amrita Institute of Medical sciences Kochi, Kerala, India.

Submitted April 3, 2007; accepted February 18, 2008.No benefits or funds were received in support of the study.Reprint requests: Uday Pawar, Diploma Ortho, Department of

Orthopaedics, P D Hinduja National Hospital, Veer SavarkarMarg, Mahim, Mumbai 400016, India.

© 2009 Elsevier Inc. All rights reserved.0883-5403/08/2404-0022$36.00/0doi:10.1016/j.arth.2008.02.017

636

been no quantification of the hypovascularity or theduration of transient hypovascularity to date [3-6].

Inour institute, of 45 lateral releases in277patients,none of the patients had clinical and radiologicalevidence of osteonecrosis or patellar fracture. There-fore, we attempted the study to quantify the patellarvascularity and its association with lateral release.

This was a prospective, nonrandomized controlstudy using Tc-99m MDP bone scans.

Materials and methods

Fifty-nine patients (72 knees) who underwenttotal knee arthroplasty between August 2005 andDecember 2006 were included. Ten were men and49 were women; age was between 52 and 86 years(average, 67 years). Preoperative diagnosis wasprimary osteoarthrosis in 55 and rheumatoid arthri-tis in 17. Preoperative and postoperative radiographsincluded weight-bearing AP, Lateral and Skylineviews with the knee in 60 degrees flexion (Fig. 1).

Fig. 1. Showing anteroposterior, lateral, and 60° skyline views.

Scintigraphic Assessment of Patellar Viability in TKA After Lateral Release � Pawar et al 637

Preoperative bone scans were done between 0and 3 days before surgery and between 7 and 10days postoperative and repeated between 8 and 10weeks if the immediate postoperative scans showedhypovascularity. The x-rays were evaluated forevidence of osteonecrosis and fractures. Clinicalevaluation included evaluation for anterior kneepain, maltracking, and difficulty in getting up from achair or descending stairs.

Fig. 2. Standard 3-ph

All patients had a standard medial parapatellarapproach and maltracking was assessed with the“no thumbs test” with a very low threshold forlateral release. The lateral release was done 1 cmlateral to patella and patellar quadriceps tendonswith no attempt at saving the superior lateralgeniculate artery. The 3-phase scintigraphy wasdone using intravenous Technetium-99m methy-lene diphosphonate, followed by 60-second vas-

ase bone scan.

Fig. 3. Region of interest for quantitative assessment.

Table 1. Study Data 2 × 2 Table

Lateralreleasenot done

Lateralreleasedone Total

atellavascularity

Notaffected

31 (86.1%) 22 (61.1%) 53 (73.6%)

Affected 5 (13.9%) 14 (38.9%) 19 (26.4%)otal 36 (100%) 36 (100%) 72 (100%)

638 The Journal of Arthroplasty Vol. 24 No. 4 June 2009

cular phase, 5-minute soft tissue phase, and 3-hour skeletal phase. The patellae were imaged ina lateral and external oblique position using adual-head camera. Fig. 2 shows the standard 3-phase scans. The bone scans were interpretedindependently by 2 nuclear medicine physicians,unaware of the extent of surgery. This wasqualitatively assessed by visual assessment of theradioactive uptake as described by Wetzner andRitter [1]. For quantitative assessment, regions ofinterest were marked on the target area patellaand nontarget area femoral shaft and the ratioswere calculated separately for the preoperativeand postoperative scans [7] (Fig. 3). A trainedtechnologist of nuclear medicine who was una-

Fig. 4. Case of transient hypovascularity documented on bone scbone scan.

P

T

ware of the consultants interpretation did theregion of marking, and the uptake of Tc-99mMDP in each of the areas was quantified as theradioactive counts for calculating the ratio. Fig. 4shows an example of transient ischemia seen at1 week postoperative and which returned to normalat the 8-week postoperative scans.

Results

Of the total number of 72 knees, 14 of 36 lateralreleases resulted in hypovascularity as compared to5 of 36 without lateral release. Visual interpretation(qualitative) concurred with the quantification in allcases. None of the patients had patellofemoralsymptoms at the 3 and 6 months follow-up, andpresence of any symptoms were independent oflateral release. There was no difference in thepostoperative knee society score (range, 86-94)between the patients who did or did not have thelateral release. On radiological evaluation, therewere no patella fractures or sclerosis at 6 monthspostoperative. The odds ratio for lateral release vspatellar vascularity was 3.95, which meant that therelative risk for getting a hypovascular patella wasapproximately 4 times (Table 1). The Fisher exact

an which returned to near normal at 9-week postoperative

Scintigraphic Assessment of Patellar Viability in TKA After Lateral Release � Pawar et al 639

test (2-tailed) showed that the association of patellarvascularity with lateral release was significant (P =.031). The difference in the target to nontarget ratiobetween the preoperative and postoperative scanswere calculated, and the Student t test (paired) wasapplied on which the P values (.155 and less than.001) were found to be insignificant (Table 2). Thestatistical association of variables such as patellarresurfacement, patelloplasty, and fat pad excisiontested by the χ2 test were insignificant (P values.218, 1.0, and .100, respectively). All 19 kneeswhich showed hypovascularity were found to havenear normal vascularity by quantitative assessmentat 8 to 10 weeks of scan.

ig. 5. Blood supply disruption during lateral releaselong with a medial parapatellar approach in totalnee arthroplasty.

Discussion

The standard medial parapatellar approach withlateral release sacrifices all the major blood supply ofthe patella except possibly the recurrent branch ofthe anterior tibial artery. (Fig. 5). The fat padexcision could further damage the blood supply.The association of osteonecrosis with lateral releasehas been reported by numerous authors (Cameronand Fedorkow [4], Clayton and Thirpathi [5],Kayler and Lyttle [6], Scott et al [3], and Wetzner[1]). Scott et al [3] suggested that the resultingosteonecrosis could lead to patellar fracture. Thiswas contradicted by Mcmahon et al [8]. Ritter et alin 1987 and 1989 reported that the osteonecrosiswas not related to the lateral release and the patellarfracture was more common when lateral releasewas not done. However he contradicted this in 1996and 1999 and reported that the patellar fracture wasthe only complication affected by lateral release butshowed the preservation of superior lateral genicu-late artery made no effect on the incidence of patellafracture [9]. Gelfer et al [10] reported that transientpatella ischemia occurred in 13.5% of individualsand that it might be related to the symptoms of theanterior knee pain. In this study, association oflateral release with transient patellar hypovascular-ity was significant; all of them recovered to near

Table 2. Statistical relation between lateral releaseand vascularity

Lateralrelease

Vascularity Studentt test (paired) PMean SD

Done(36 cases)

−0.0383 0.6920 0.33 Nonsignificant

Not done(36 cases)

0.7022 0.7549 5.58 b.001

Fak

normal at 8 weeks. We believe the objectivequantification method calculating the target tonon-target ratio was more accurate other than thequalitative visual interpretation method describedearlier. The methodology used here could eliminatethe errors due to variability in limb position and thetime intervals from drug administration to imaging.However, the study is short-term, but as thevascularity returns to near normal, the chances oflong-term patellar complication as a result of lateralrelease may be minimal.

Conclusion

Scintigraphy with quantification is an objectivedocumentation of patellar vascularity. The associa-tion of lateral release and transient patellar ischemiawas insignificant with about 25% risk.

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