The Journal of Arthroplasty Vol. 24 No. 5 2009
Quantification of Effect of Sequential PosteromedialRelease on Flexion and Extension Gaps
A Computer-Assisted Study in Cadaveric Knees
Arun Mullaji, FRCS Ed, MCh Orth, MS Orth, Amit Sharma, MS Orth, DNB Orth,Satyajit Marawar, MS Orth, and Raj Kanna, MS Orth
Abstract: A novel sequence of posteromedial release consistent with surgicaltechnique of total knee arthroplasty was performed in 15 cadaveric knees. Medialand lateral flexion and extension gaps were measured after each step of the releaseusing a computed tomography–free computer navigation system. A spring-loadeddistractor and a manual distractor were used to distract the joint. Posterior cruciateligament release increased flexion more than extension gap; deep medial collateralligament release had a negligible effect; semimembranosus release increased theflexion gap medially; reduction osteotomy increased medial flexion and extensiongaps; superficial medial collateral ligament release increased medial joint gap more inflexion and caused severe instability. This sequence of release led to incremental anddifferential effects on flexion-extension gaps and has implications in correcting varusdeformity. Key words: posteromedial release, knee, computer navigation.© 2009 Elsevier Inc. All rights reserved.
Ligaments and soft tissues on the medial side of theknee undergo contracture in varus deformity andrequire release to achieve neutral limb alignment[1-12]. Satisfactory ligament release is achievedwhen the ligaments are of equal length on themedial and lateral side of the knee with themechanical axis of the limb passing throughthe center or slightly lateral to the center of theknee [3]. Ligament balancing improves polyethy-lene wear also [8,9].
From the Department of Orthopaedic Surgery, Breach CandyHospital, Mumbai, India.
Submitted October 16, 2007; accepted March 22, 2008.Benefits or funds were received in partial or total support of
the research material described in this article from DePuy India.Reprint requests: Arun Mullaji, FRCS Ed, MCh Orth, MS Orth,
The Arthritis Clinic, 101, Cornelian, Kemp's Corner, CumballaHill, Mumbai 400036, India.
© 2009 Elsevier Inc. All rights reserved.0883-5403/08/2405-0021$36.00/0doi:10.1016/j.arth.2008.03.018
795
With the advent of navigated total knee arthro-plasty (TKA), the mechanical axis of femur and tibiacan be assessed individually intraoperatively with anaccuracy of 1° [5,6]. Similarly, change in joint gapcan be measured with an accuracy of 1 mm [5,6].After performing distal femoral and tibial resectionsperpendicular to their respective mechanical axes,equal medial and lateral gaps are desired, both inflexion and in extension, to achieve neutral align-ment of the limb and balanced joint gaps ensuring astable joint.
Various studies have assessed the effect of medialligament release on final limb alignment and medio-lateral gap in flexion and extension [1,3,5-15,20].However, only 2 publications (both from the samecenter) were based on cases conducted usingcomputer navigation [5,6]. It has been found thata different sequence of soft tissue release may havedifferent effects on the joint gap. In previous studies,posterior cruciate ligament (PCL) release was doneat a later stage in the release sequence [1,3,5-15].
796 The Journal of Arthroplasty Vol. 24 No. 5 August 2009
We adopted a technique of PCL release at an earlystage, which is usually the case during TKA withPCL-substituting implants. In addition, PCL releasehas been found to have a significant impact onmedial and lateral joint space, and varus deformityat the knee, and if PCL is released early, it may limitthe amount of release required in the later stage ofthe release sequence for correction of varus defor-mity and joint gap equalization [3,12,16,17]. Noneof the previous studies have compared the resultsusing different distraction devices.The aims of this study were
(1) To study the effect of a specific sequence ofposteromedial release with early PCL release,as described by Mullaji et al [18] for severevarus deformity, on medial and lateral flexionand extension gaps using 2 different typesof distractors.
(2) To assess the effect of these releases onalignment of the limb in extension.
(3) To compare the results obtained with a manualdistractor with those using a spring-loadeddistractor having constant distraction force.
Materials and Methods
Fifteen cadaveric knees were studied in 8 freshcadavers (all male). One knee from the first cadaverwas not included in the study because it was thefirst knee in the study, and data recording protocolwas set using that knee. Cadavers were stored at−20°C before the study. On the night before thestudy, cadavers were placed at 4°C and then werekept at room temperature for 2 hours before thestudy. None of the limbs had signs of previoustrauma, or surgery involving the joint under studyor ipsilateral ankle or hip. There was no limb withpreexisting flexion or varus-valgus deformity.Whole cadavers were used for the study ratherthan isolated limbs. No soft tissue was removedfrom the limb. Approval of the local ethicscommittee was taken for the study.An image-free navigation system (Ci CT-free
navigation, Depuy I-Orthopaedics, Munich, Ger-many) was used. This navigation system is based onan optical tracking unit, which detects reflectingmarker spheres attached to the bone and instru-ments by an infrared camera system.All procedures were performed by the senior
surgeon. A mid-line skin incision was taken andmedial parapatellar arthrotomy was performed toexpose the knee joint. The patella was evertedlaterally and the distal end of femur and proximal
end of the tibia were exposed. The anterior cruciateligament (ACL) and both menisci were excised. Tworeference arrays with passive navigation markerspheres were attached rigidly to the distal third ofthe femur and proximal third of the tibia each withthe help of 2 pins through separate stab incisions.Registration of various landmarks, surface topogra-phy, and determination of the hip center by pivotingthe entire limb were carried out as directed in thenavigation system manual. Proximal tibial resectionwas performed using navigation to resect 8 mm ofthe upper tibia as measured from the lateral plateauwith a 3° slope to allow the insertion of manual andspring-loaded distractors. Special care was taken notto disturb the tibial attachment of the PCL whileperforming the osteotomy.
Medial and lateral joint gap measurements weremade at first using the manual distractor. This wasakin to a dual laminar spreader. The manualdistractor had a base plate (shaped like a tibialtray) which sat on the resected tibial surface, butthere were 2 independent top plates—one each formedial and lateral sides which were not connectedto one another and could be distracted separately bythe surgeon and maintain the distraction. Medialand lateral gaps displayed on the monitor werenoted after manually distracting the joint surfacessuch that the surgeon felt equal pressure on thethumb screws used to distract the medial and lateralcondyles. This was done first with the knee flexed to90°, with the thigh supported by an assistant, andthen in extension with the surgeon supporting thehorizontal leg with a hand placed beneath the heel.A spring-loaded distractor (Depuy, Leeds, UK) wasthen placed in the joint space and the entireprocedure was repeated in flexion and then inextension. The spring-loaded distractor loaded themedial and lateral compartments separately andconstantly with 2 springs each exerting a load of 12kg via 2 parallel plates pivoted at the center.
The patella was everted to allow insertion of thedistractors. However, it was reduced in place beforethe measurements were taken with the spring-loaded distractor (which did not have a handle andwas the shape of the tibial trial tray), but not withthe manual distractor which had a handle. Align-ment of the limb was also noted in the frontal planein extension. All measurements were repeatedthrice at every step and the mean value was takenfor that particular step. The senior surgeon wasunaware of the readings which were noted by one ofthe authors.
The sequence of soft tissue release performed wasas described byMullaji et al [18] for the correction ofsevere varus deformity and was deployed after the
Tab
le1.
Med
ialGap
After
Seq
uen
tial
Relea
se
Distractoran
dLim
bPosition
ACLRelea
sePCLRelea
seDee
pMCLRelea
seSem
imem
bran
osus
Relea
seMed
ialOsteo
tomy
Pes
Anserinus
Relea
seSupe
rficialMCL
Relea
se
Man
ual
distractor
90°Flexion
5.8
±2.4
8.9
±1.6†(3.1
±1.8)
9.0
±2.0
(0.2
±0.7)
9.8
±2.1†(0.8
±0.7)
10.4
±2.1*(0.6
±0.6)
11.9
±2.1*(1.5
±2.5)
18.9
±3.6†(7.0
±2.8)
Extension
7.1
±3.2
7.9
±3.1*(0.8
±0.6)
8.0
±3.4
(0.2
±0.8)
7.6
±2.9
(−0.4
±0.8)
8.8
±3.2*(1.1
±1.2)
9.2
±3.6
(0.4
±1.0)
12.0
±4.3†(2.8
±1.5)
Spring-load
eddistractor
90°Flexion
6.5
±2.4
9.4
±2.2†(2.9
±1.3)
9.4
±2.2
(0.7
±2.8)
9.9
±2.2*(−0.1
±2.7)
10.5
±1.9*(0.7
±0.7)
11.2
±3.0
(0.7
±1.9)
15.0
±1.9†(3.7
±2.0)
Extension
7.58±3.12
7.8
±3.0
(0.2
±0.7)
7.7
±3.2
(−0.1
±0.9)
7.8
±3.3
(0.1
±0.6)
8.4
±3.6*(0.7
±0.8)
9.5
±3.8
(1.1
±2.6)
10.8
±3.6
(1.3
±3.2)
Allva
lues
arein
millim
eters(m
ean±SD).
Values
inparen
theses
den
ote
chan
gein
thejointga
pfrom
thepreviousstep
.* P
b.05statistically
sign
ifican
tlydifferentfrom
previousstep
.†Pb.001
statistically
very
sign
ifican
tlydifferentfrom
previousstep
.
Quantification of Effect of Sequential Posteromedial Release � Mullaji et al 797
initial excision of the ACL, menisci, and proximaltibial resection. Two methods of separating softtissue from their bony attachment were used: onewas sharply transecting the fibers (such as for thePCL and pes), and the other was detaching the fibersindirectly by taking them off from the bone incontinuity with a sleeve of their periosteal attach-ment, that is, subperiosteal release.Step 1—The PCL was sharply transected from its
femoral attachment and then excised with the helpof a scalpel.Step 2—The deep medial collateral ligament
(deep MCL) was subperiosteally released from themedial rim of the tibia.Step 3—The semimembranosus was released
subperiosteally, using a scalpel, from the postero-medial aspect of the tibia.Step 4—Reduction osteotomy [18] was per-
formed by osteotomizing a 1-cm-wide arc of theposteromedial corner of the proximal tibia using a10-mm osteotome. This step was performed tomimic the effect of excising medial osteophytesand the posteromedial tibial overhang.Step 5—Release of the pes anserinus was per-
formed by vertically dividing the broad insertion ofthe pes just posterior to its insertion on the tibia,taking care to protect the fibers of the superficialMCL passing beneath it.Step 6—Release of the superficial MCL was
performed by subperiosteally elevating its insertionalong the upper medial tibial surface for a distance ofabout 6 to 8 cm below the joint line.Data were recorded in an Excel sheet (Microsoft,
Redmond, Wash) and subjected to statistical analy-sis. Paired t test was used to study the statisticaldifference between groups. Statistical significancewas determined at P b .05.The medial and lateral flexion and extension gaps
(in millimeters) and alignment (in degrees) werecompared as follows:
(1) Change in the gap after each step of therelease. This was done for gaps medially andlaterally, with manual and spring-loaded dis-tractor, and in 90° flexion and extension.
(2) Comparison of gaps and changes in gap aftereach release in flexion vs extension (mediallyand laterally, with manual and spring-loadeddistractor).
(3) Comparison of gaps and change in gapmediallyvs laterally (with manual and spring-loadeddistractor, in extension and 90° flexion).
(4) Comparison of gaps using manual vs spring-loaded distractor (medially and laterally, in 90°flexion and extension).
Table . Alignment of the Limb After Sequential Release
Distractor and Limb Position ACL Release PCL Release Deep MCL ReleaseSemimembranosus
Release Medial OsteotomyPes Anserinus
ReleaseSuperficial MCL
Release
Manual distractor—Extension −0.1 ± 2.3 −0.8 ± 2.2 (0.1 ± 1.1 −0.3 ± 2.5 (0.4 ± 1.2) −0.1 ± 2.3 (0.3 ± 1.3) 0.5 ± 1.9 (0.5 ± 1.3) 0.7 ± 1.9 (0.2 ± 1.0) 3.1 ± 4.9 (2.9 ± 4.5)Spring-loaded distractor—
Extension−0.1 ± 3.1 −0.3 ± 2.7 (−0.2 ± 1 0.2 ± 2.9 (0.5 ± 1.7) 0.2 ± 3.3 (−0.3 ± 2.2) 0.7 ± 3.7 (0.3 ± 1.7) 1.3 ± 4.2 (0.7 ± 1.8) 4.6 ± 4.8 † (3.2 ± 3.0)
All values are in degrees (mean ± SD).Values in parentheses denote change in the alignment from the revious step.Negative values denote change toward varus and positive value hange toward valgus alignment.*P b .05 statistically significantly different from previous step.†P b .001 statistically very significantly different from previous ep.
able 2. Lateral Gap After Sequential Release
Distractor and LimbPosition ACL Release PCL Release Dee MCL Release
SemimembranosusRelease Medial Osteotomy
Pes AnserinusRelease
Superficial MCLRelease
Manual distractor90° Flexion 11.0 ± 3.1 4.2 ± 2.1† (3.1 ± 2.6) 14.0 2.5 (−0.1 ± 1.1) 14.5 ± 2.5† (−0.5 ± 0.9) 14.7 ± 2.5 (0.2 ± 0.7) 15.2 ± 2.6 (0.6 ± 0.9) 16.3 ± 2.6 † (1.1 ± 1.9)Extension 10.5 ± 3.2 11.6 ± 3.0 (1.1 ± 0.9) 11.5 3.2 (−0.1 ± 0.9) 10.9 ± 2.7 (−0.5 ± 1.2) 11.7 ± 2.6 (0.7 ± 1.0) 12.0 ± 2.9 (0.3 ± 0.8) 12.4 ± 3.8† (0.5 ± 3.1)Spring-loaded distractor90° Flexion 12.0 ± 2.9 4.9 ± 2.5† (2.8 ± 2.4) 14.2 3.5 (−0.7 ± 1.5) 14.4 ± 2.5 (0.2 ± 1.4) 14.8 ± 2.1 (0.4 ± 0.8) 14.6 ± 1.9 (−0.3 ± 0.9) 13.7 ± 1.3 (−0.8 ± 1.1)Extension 11.6 ± 3.2 12.1 ± 3.3 (1.3 ± 3.2) 11.1 3.4 ()0.9 ± 1.4) 11.3 ± 3.6 (0.2 ± 0.9) 11.1 ± 3.6 (−0.2 ± 1.1) 11.0 ± 3.5 (−0.1 ± 1.0) 10.7 ± 3.2 (−0.3 ± 1.7)
All values are in millimeters (mean ± SD).Values in parentheses denote change in the joint gap from the p vious step.*P b .05 statistically significantly different from previous step.†P b .001 statistically very significantly different from previous ep.
798The
Journalo
fArthro
plasty
Vol.24
No.5Aug
ust2009
3
).3)
ps c
st
T
p
±±
±±
re
st
Fig. 1. Medial joint space, in 90° flexion, using manual distractor.
Quantification of Effect of Sequential Posteromedial Release � Mullaji et al 799
(5) Change in alignment after each release (inextension only, with manual and spring-loaded distractor).
(6) Comparison of alignment between manualand spring-loaded distractor (after each stepin extension only).
Results
These are summarized in Tables 1-3, and Figs. 1-4.
Effect of Releases on Medial and Lateral GapsUsing the Manual Distractor
There was progressive increase in the medial jointspace after sequential medial release in flexion as
Fig. 2. Medial joint space in 90° flexio
well as extension. However, this progress was notconsistent on the lateral side. After PCL release,there was a significant increase in joint gap, mediallyas well laterally. However, these changes weresignificantly higher in flexion (mean, 3.1 mm)than in extension (mean, 0.8 mm) (P .001, Studentt test). There was a statistically significant opening ofthe joint gap after semimembranosus release inflexion (P .001, Student t test), medially (0.8 mm)more than laterally (0.5 mm). However, there wasno effect of this release on joint gap in extension.After reduction osteotomy of the tibial plateau, jointgap increased in extension (P b .05, Student t test),both on the medial (1.2 mm) and on lateral side (0.8mm). In flexion, however, this increase was seen onmedial side only (0.6 mm). After pes anserine
n, using spring-loaded distractor.
Fig. 3. Medial joint space in extension, using manual distractor.
800 The Journal of Arthroplasty Vol. 24 No. 5 August 2009
release, joint gap increased substantially, medially,and laterally, in flexion only (1.5 mm, P b .05,Student t test). Release of superficial MCL producedthe greatest effect on medial gap in flexion (7.0 mm)as well as in extension (2.8 mm, P b .001, Student ttest). This effect was more evident in flexion. Therewas some opening on the lateral side also (1.1 mmin flexion, 0.5 mm in extension).
Effect of Release on Medial and Lateral GapsUsing the Spring-Loaded Distractor
With the spring-loaded distractor also, there wasprogressive increase in the joint space on themedial side after each successive release, both inflexion and in extension. However, joint space on
Fig. 4. Medial joint space in extension
the lateral side did not show similar consistency.With the spring-loaded distractor, PCL releaseproduced significant change in joint gap medially(2.9 mm, P ≪ .001, Student t test) and laterally(2.8 mm, P b .001, Student t test) in flexion.However, there was no effect of PCL release onjoint gap in extension. Semimembranosus releaseproduced an increase in medial joint gap in flexion(0.6 mm, P .006, Student t test). Medial osteotomyof the tibia produced an increase in medial gap inflexion (0.7 mm, P .004, Student t test) andextension (0.7 mm, P .006, Student t test). Aftersuperficial MCL release, there was a very signifi-cant opening of medial (3.7 mm, P ≪ .001, Studentt test) joint gap in flexion. However, no effect wasseen in extension.
, using spring-loaded distractor.
Quantification of Effect of Sequential Posteromedial Release � Mullaji et al 801
Comparison of Gaps and Changes in Gap AfterEach Step of Release in Flexion vs ExtensionWith the Manual Distractor
There was a significant difference between jointgap on medial side in flexion and extension aftersemimembranosus release (2.2 mm, P .021, Studentt test), pes release (2.7 mm, P .008, Student t test),and after superficial MCL release (6.9 mm, P b .001,Student t test) with the joint gap being higher inflexion. On the lateral side, on the other hand, jointgap was higher in flexion with all releases exceptafter ACL release (P .653, Student t test). Thehighest difference was again after superficial MCLrelease (3.9 mm, P .001, Student t test).Similarly, change in medial joint gap, from one
release to the next release, was statistically sig-nificantly different between flexion and extensionafter PCL release (2.3 mm, P .001, Student t test),semimembranosus release (1.2 mm, P .001, Stu-dent t test), and after superficial MCL release(4.2 mm, P b .001, Student t test) with gap changesbeing higher in flexion. On the lateral side, thesedifferences were present after PCL release in flexion(2.0 mm, P .018, Student t test). It is evident thatthe PCL release produces more joint space changein flexion than in extension.
Comparison of Gaps and Change in Gap AfterEach Step in Flexion vs Extension With theSpring-Loaded Distractor
With the spring-loaded distractor, joint gap hadhigher values on the medial side in flexion afterdeep MCL release (1.7 mm, P .03, Student t test),medial osteotomy of the tibia (2.1 mm, P .033,Student t test), and superficial MCL release (4.2mm, P .002, Student t test). On the lateral side, jointgap had a higher value in flexion at every stepexcept after ACL release, similar to findings with themanual distractor.Gap changes from one step to the next step were
highly significant on the medial side after PCLrelease (2.5 mm, P ≪ .001, Student t test) and aftersuperficial MCL release (2.4 mm, P .034, Studentt test) on the medial side and after PCL release(1.5 mm, P .019, Student t test) on the lateral sidewith the spring-loaded distractor, with openingbeing more in flexion than in extension.
Comparison of Medial and Lateral Joint GapsWith the Manual Distractor
Lateral joint gaps were larger than the medialgaps after every step in flexion and extension (P ≪.001, Student t test) except after superficial MCL
release when the medial joint gap exceeded thelateral gap by 2.6 mm (P .007, Student t test) inflexion; there was no difference in medial andlateral joint gaps in extension.
Change in gap was statistically significantlydifferent between the medial and lateral side aftermedial osteotomy of the tibia (0.4 mm, P .034,Student t test) and superficial MCL release (5.9 mm,P b .001, Student t test) in flexion, and aftersuperficial MCL release (2.3 mm, P .03, Student ttest) in extension, with the joint opening beingmoreon the medial side.
Comparison of Medial and Lateral Joint GapsWith the Spring-Loaded Distractor
Lateral joint gap was significantly greater thanmedial joint gap (P ≪ .001, Student t test) at everystep in flexion and extension except after superficialMCL release in flexion when the medial joint gaphad a higher value in flexion (1.3 mm, P .015,Student t test). In extension, there was no differencebetween medial and lateral joint gap after pes andsuperficial MCL release.
Regarding change in joint gap from one step to thenext step, change on the medial side was muchhigher (4.5 mm, P .001, Student t test) than on thelateral side in flexion after superficial MCL release.In extension, on the other hand, difference inchange was evident after deep MCL (0.8 mm,P .006, Student t test) and medial osteotomy(0.9 mm, P .018, Student t test) only, with thechange being higher on the medial side.
Change in Alignment With Sequential Release—Manual vs Spring-Loaded Distractor
Although there was progressive change in align-ment from varus to valgus with each step, there wasno statistically significant difference in the value ofalignment before and after any step with both typesof distractors except after superficial MCL releasewith the spring-loaded distractor (P .001, Studentt test).
Comparison Between Manual andSpring-Loaded Distractor
There was no statistically significant differencebetween both types of distractors when the values ofmedial and lateral joint gaps were compared afterevery step of the release. However, after pes release,in flexion, the medial joint gap increased slightlymore with the manual distractor (1.5 mm vs 0.7 mmwith the spring-loaded distractor). Similarly, aftersuperficial MCL release, there was a significant
802 The Journal of Arthroplasty Vol. 24 No. 5 August 2009
difference in the values of the joint gap betweenboth distractors, medially as well as laterally, inflexion (P b .001, Student t test) and extension (P b.05, Student t test), with the values being higherwith the manual distractor. The difference in gapchange between both distractors was evident afterpes and superficial MCL release on medial andlateral side, in flexion only.
Discussion
Limb alignment is important for the long-termoutcome of TKA [1,4,7,9,12]. Ligament balancing isan integral part of knee arthroplasty to achieveneutral limb alignment and equal tibio-femoral jointgaps both medially and laterally during the entirerange of motion [1-3,8-10,12]. Computer naviga-tion has been proven to detect changes in alignmentto an accuracy of 1° and changes in the joint gap to1 mm [5,6].Three different layers of soft tissues are present on
the medial side of the knee [19]. These soft tissuesmay undergo contracture in a varus knee [1-12]. Asequential release of the soft tissues and ligamentshas been recommended [1,3,5,6,13,20] to achieveequal gaps on the medial and lateral sides. In hasbeen found that release of different parts of aligament can lead to unequal changes in flexionand extension gaps [10,11,15].Most of the previous studies were conducted
using either isolated bones with intact ligaments andsoft tissues around the knee [7,10,13-15,21] ordismembered limbs sectioned above and below theknee with intact skin and other soft tissues[11,17,20,22-24]. We believe that soft tissueremoval from the lower limb may influence theeffect of various releases on alignment and joint gap.Hence whole limbs were used in our study, whichwas also necessary for registration of navigationdata. Only 2 studies used intact lower limbs withnavigation [5,6].In previous studies, various types of joint dis-
tractors were used on an experimental basis[6,12,22,25]. In the present study, the senior authorused the same manual distractor which he has usedin more than 2000 TKA and tried to comparequantitatively the results obtained with the spring-loaded distractor which exerts a fixed amount ofdistraction force across the joint. Luring et al, in theirstudy using the computer navigation, either did notmention the amount of varus-valgus force appliedduring the experimentation [5] or applied 150-N mforce in extension and 90-N m in flexion [6]. Thereason behind the use of 2 different distraction
forces (which appear quite excessive to the authorsof this study) in different positions of the knee wasnot specified; it may lead to different results with thesame release in flexion and extension due to thedifference in the amount of force applied in differentpositions. A manually operated distractor was usedwhich acts as a lamina spreader on the medial andlateral side separately and simultaneously. As thisdistractor depends more on surgeons' “feel” to assesswhether they are applying an equal amount ofdistraction force on the medial and lateral sides, weused another type of distractor which exerted a fixedamount of force (24 kg) across the joint surfaces. Onstatistical assessment, it was found that there was nodifference in the joint gap between both types ofdistractors except after the final releases when themanual distractor gave significantly higher values.These differences, though, were statistically signifi-cant on the medial and lateral side, in both flexionand extension, and were more significant on themedial side and in flexion. It has been proven thatafter the complete release of the superficial MCL, thejoint becomes quite unstable medially [5,6,12]. Wefound that we were able to open the medial jointspace to a large degree with the manual distractorafter superficial MCL release, whereas the spring-loaded distractor had a limit of opening equivalentto its maximum thickness after full opening. Thismay be the potential cause of the difference in thevalues of medial joint gap between both types ofdistractors after final releases. Similarly, gap changesafter pes and superficial MCL release were signifi-cantly different between the 2 distractors in flexiononly.
Different sequences of soft tissue releases havebeen used in the past [1,3,5-15,20]. We have used asequence of soft tissue release technique describedby Mullaji et al [18] in which the PCL was releasedat an early stage as compared to previous studies inwhich it was released later. In the senior author'sopinion, it is more practical to release PCL at an earlystage when one is using a PCL-substituting implant,particularly for significant deformities. Posteriorcruciate ligament removal has been found to makeligament balancing a simpler task, and it can beeasily substituted by a posterior post [21]. AlthoughDorr et al [26] found that PCL-sacrificing TKAs havegreater medial loading, which may lead to excessivepolyethylene wear, and cautioned against release ofPCL, it has been found that the major role of PCLwas maintenance of joint gap in flexion rather thanreproduction of normal knee kinematics [25]. Inaddition, there is not much clinical and radiologicaldifference between PCL-retaining or -substitutingimplants [25]. Teeny et al [9] found that PCL release
Quantification of Effect of Sequential Posteromedial Release � Mullaji et al 803
may not have any effect on correction of varusdeformity. However, PCL may be contracted invarus knees [3,16], which can cause femoral rollback on tibial implant. It is also advocated that PCLrelease, when combined with medial release, willproduce better correction of deformity in varusknees, and, hence, we believe that the PCL shouldbe released at an early stage [12,17].There was a substantial increase in the medial as
well as lateral gap after PCL release, in flexion aswell as in extension with the manual and spring-loaded distractor. However, the increase in jointgap was more on the medial side and in flexion. Itwas found that PCL has more abduction restrainingeffect in 90° of flexion than in extension [5-7,11,22]. Kadoya et al [25] found that PCL releasedoes not cause medial joint opening in extension,but has this effect in flexion. The effect of PCLrelease on joint gap was more in flexion than inextension in our study as was found in previousstudies [5-7,12,17,20,21,24,25]. This may be due tothe fact that in extension the posterior capsule andother structures are tight and provide stabilityagainst valgus force [14]. This has implications indeciding the extent of distal femoral resectionwhich may have to be adjusted accordingly.Presence of posterior osteophytes and their excisionwould also impact on the extension gap; however,for obvious reasons this effect could not beestablished in this study.After semimembranosus release, there was a
significant difference in the medial and lateral gapsin 90° of flexion. However, there was no change inextension. This finding signifies that the effect ofsemimembranosus release causes an increase inflexion gap, medially more than laterally. Reductionosteotomy of the posteromedial overhang of thetibia led to an increase in the joint gap on the medialside only, in extension as well as in flexion, withboth types of distractor. Yagishita et al [12] alsofound an increase in the medial gap in extensionafter medial osteophyte removal.Release of superficial MCL from the tibial attach-
ment had the maximum effect on change in jointgap as expected. This is because the superficial MCLis the major stabilizing structure on the medial sideof the knee against valgus stress in flexion as well asin extension [13,15,20]. Release of superficial MCLcaused an opening of the joint gap medially morethan laterally, with both types of distractor, and ledto severe instability. These changes were greater inflexion than in extension as was found in previousstudies also [13,15]. However, Luring et al [5] andMatsueda et al [7] found that the effect of superficialMCL release led to a greater increase in the joint gap
in extension. There was no significant effect of deepMCL release as was found in previous studies[13,15].
The joint gap was consistently greater in flexionthan in extension on the medial and lateral sides.Similarly, change in the joint gap was also greater inflexion than in extension after most steps of therelease. This may be due to the fact that the kneejoint is maximally stable against varus-valgus forcesin full extension owing to stretching of posteriorcapsule and other soft tissue structures across theposterior aspect of the knee [20]. This finding issimilar to previous work by Kadoya et al [25] onpatients with osteoarthritic knees. They also foundthat gap changes, although higher on the medialside, were not statistically significantly differentfrom the joint gap changes on the lateral side aswas found in our study. Medial joint gap changeswere found higher than on the lateral side [17].
It was found that the actual lateral gap consis-tently exceeded the medial gap even after sequentialreleases until the superficial MCL was releasedwhen the medial gap was significantly higher thanthe lateral gap in flexion. However, in extension,there was no difference in medial and lateral gapseven after superficial MCL release. This observationis similar to the finding by Kadoya et al [25] andYagishita et al [12]. With the sequential release ofmedial soft tissues, lateral joint space also increased.This may be due to the overall effect of medial softtissue release on the entire joint space [12].
There was progressive change in the alignment,though not statistically significant, from varus tovalgus after each release. After superficial MCLrelease, alignment changed to marked valgus aswas found in previous studies [5,6,12]. Clearly, thisstep must be avoided where possible to preventmajor instability.
Luring et al [5,6] did a similar study using thecadaveric model with computer navigation. How-ever, they followed a different protocol of soft tissuerelease with the PCL being released at a very latestage [7]. They found that sequential releaseproduced the desired increase in alignment andtibio-femoral gap after every release on the medialside, which is consistent with our study [12]. Thisincrease was maximum after a complete release ofsuperficial MCL. However, in one of their studies[5], they used a varus-valgus force, without anystandardization on the amount of force applied.They could not find a statistical increase in the lateraljoint space after any release in contrast to our studywhere we found that lateral joint also tended toincrease statistically after most of the releases on themedial side as was found in some other studies
804 The Journal of Arthroplasty Vol. 24 No. 5 August 2009
[7,12]. Change in the medial gap was most markedin flexion after the release of the superficial MCL,whereas in extension, it was significant after everyrelease, which signifies that release of the superficialMCL has more of a varus correcting force and opensthe medial joint more in flexion than in extension.The authors stated that use of laminar spreaders isnot a reliable method to check for tension inligaments while measuring joint gap [6].Markolf et al [20], in their study using cadaveric
limbs, found the knee more stable in full extensionand hence best for assessment of the effect ofligament release on alignment. Significant laxityon combined release of cruciate and superficial MCLwas found [14,20]. They also stated that release ofmore than 2 structures simultaneously producesinstability of the joint. In our study, superficial MCLrelease produced marked instability of the knee jointon the medial side. Grood et al [13] also found thatrelease of MCL alone was not very effective incorrecting the varus deformity. It needed to becombined with cruciate release for varus correction.Matsueda et al [7] used a different sequence of
soft tissue release which was followed by otherauthors also [5,6]. They released PCL at a late stage.They used an optical encoder for change in angle ofthe limb with the use of 10-N m varus and valgusforce and a digital caliper for the changes in joint gapwith 53-N m distraction force. Medial collateralligament was found to have more change in jointgap in extension in contrast to our and other studies[13,15]. The authors did not find significant changeseither in the lateral joint gap with progressive medialrelease. They quantified the amount of release bythe length of soft tissue release from the joint line asit was difficult to identify individual structures,especially in deformed varus knees. They alsospecified that they used this sequence because itwas the preferred sequence of soft tissue release thatthey use intra-operatively and said that differentsurgeons may use different release sequences whichmay produce different results [7,20].One criticism of our study was that the cadaveric
limbs were devoid of deformity as in the otherstudies [5,6]. The effect of a similar soft tissue releasesequence in a varus knee with contracted medialsoft tissues may be different from the present study[12]. A study involving patients with varus defor-mities undergoing TKA is being conducted for thispurpose. In addition, there may be an effect ofpostmortem tissue lysis, storage by freezing, andchange in the state of tissue hydration in cadavericlimbs which may alter the effect of release on thejoint space [13]. It was found by Yagishita et al [12]that release of medial and posteromedial soft tissues
caused more increase in medial flexion gap inpatients with greater varus deformity than inpatients with less varus deformity. This signifiesthat, with progressive varus, the amount of softtissue contraction on the medial side increases andthe release of these structures will have an impacton the alignment of knees with greater deformity.
Summary
A previously reported sequence of soft tissuerelease for severe varus deformity was used in freshcadaveric knees. We compared medial and lateralflexion and extension gaps with a spring-loadeddistractor and a manual distractor and found nosignificant difference between the 2 devices. ThePCL was released early in the procedure and thisincreased the medial flexion gap more than theextension gap and to a greater extent than therelease of the other structures. Deep medial collat-eral ligament release had a negligible effect. Semi-membranosus release increased the flexion gapmedially to some extent only; reduction osteotomyof the tibia increased both medial flexion andextension gaps. In practice, PCL should first bereleased; if in flexion the medial side of the joint isstill “tight,” then the semimembranosus should bereleased followed by the pes, and if the medial side is“tight” in both flexion and extension, then reductionosteotomy of the tibia should be performed. Super-ficial medial collateral ligament release increasedmedial joint gap more in flexion and caused severeinstability and should not be released except inknees with recalcitrant contractures. Thus, judiciousand titrated use of the release sequence may help incorrecting deformity with the least amount ofrelease so as to restore limb alignment and yetmaintain a balanced and stable joint during TKA.
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