Characterization of knee alignment in children with mucopolysaccharidosis types I and II and outcome of treatment with guided growth

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1 J Child Orthop (205) 9: DOI 0.7/s ORIGINAL CLINICAL ARTICLE Chrcteriztion of knee lignment in children with mucopolyscchridosis types I nd II nd outcome of tretment with guided growth Elizbeth Ashby Deborh Estwood Received: 2 December 204 / Accepted: 25 My 205 / Published online: 6 June 205 The Author(s) 205. This rticle is published with open ccess t Springerlink.com Abstrct Purpose To describe knee lignment in children of different ges with severe mucopolyscchridosis (MPS) I nd II nd the outcome of tretment with guided growth in ptient subgroup. Methods This is retrospective observtionl study of 58 knees in 29 children with severe MPS I nd II. Long-leg stnding rdiogrphs were evluted to determine mechnicl xis devition, mechnicl lterl distl femorl ngle nd medil proximl tibil ngle t different ges throughout childhood. The chnge in deformity in individul children over time is reported. 20 knees in 0 ptients were treted with guided growth using eightpltes. Rdiogrphic mesurements were recorded t the time of plte insertion, t plte removl nd t yer following removl. Results At 8 yers of ge, ll MPS I children nd threequrters of MPS II children hd vlgus knee lignment. There ws deformity progression in two-thirds of MPS I knees nd hlf of MPS II knees. Guided growth corrected the deformities. There ws recurrence in most cses yer fter plte removl. Conclusions Knee deformity is common in children with severe MPS I nd II. Guided growth cn be considered where there is significnt nd/or or progressive deformity with the im of hlting progression nd correcting existing & Deborh Estwood deborh.estwood@gosh.nhs.uk Elizbeth Ashby elizbethshby@doctors.org.uk Deprtment of Orthopedic Surgery, Gret Ormond Street Hospitl for Children, Gret Ormond Street, London WCN 3JH, UK deformity nd thus minimizing the risk of gross deformity. Ptients should be wre of the high rte of recurrence nd the need for repet surgery. Keywords Mucopolyscchridoses Knee lignment Guided growth Introduction The mucopolyscchridoses (MPS) re group of lysosoml storge diseses chrcterized by the bsence, reduction or mlfunctioning of lysosoml enzyme. Cellulr glycosminoglycns (GAGs) ccumulte nd led to tissue nd multi-orgn dysfunction. There re different types of MPS bsed on the dysfunctionl enzyme. This study focuses on MPS I nd II. The prevlence of MPS I nd II is pproximtely in,000 [, 2]. MPS I is n utosoml recessive disorder chrcterized by dysfunctionl -L-iduronidse leding to ccumultion of dermtn sulphte nd heprn sulphte. MPS I is recognized s spectrum of disorders tht re split into severe nd ttenuted form; however, they re biochemiclly identicl. MPS II is n X-linked recessive disorder chrcterized by dysfunctionl iduronte sulphtse leding to ccumultion of the sme GAGs s in MPS I. MPS II encompsses spectrum of disorders tht re divided into 2 brod subtypes severe form chrcterized by the presence of cognitive impirment nd less severe form with no cognitive impirment. Infnts with MPS I nd II typiclly hve norml development for the first 6-2 months of life [3]. Without tretment, children with severe MPS I usully die in their first decde [4]. Children with ttenuted MPS I hve

2 228 J Child Orthop (205) 9: reltively norml life expectncy, but with significnt morbidity [4]. Without tretment, children with severe MPS II typiclly die in the second decde of life [5]. Those with the less severe form cn survive until their fifth or sixth decde [4]. A rnge of skeletl rdiogrphic bnormlities known s dysostosis multiplex re ssocited with MPS I [4] including hypoplstic vertebrl bodies (resulting in kyphosis nd scoliosis), poor growth of long bones, hip dysplsi nd genu vlgum [6, 7]. The rte of genu vlgum in MPS I is between 52 [8] nd70%[9]. The deformity is thought to originte from filure of ossifiction of the lterl mrgin of the proximl tibil metphysis [6]. Dysostosis multiplex is less drmtic in MPS II [0]. The incidence of genu vlgum is unknown. Hemtopoietic stem cell trnsplnttion (HSCT) is used to tret severe MPS I []. Donor cells synthesise continuous endogenous supply of the deficient enzyme leding to incresed life expectncy nd improved cognitive nd physicl function. HCST hs mortlity rte of 5 % [2]. It hs been used to tret MPS II [3] but is not usul prctice. HCST hs little effect on the musculoskeletl system [4]. Odontoid hypoplsi shows some improvement [5] but hip dysplsi nd genu vlgum continue to progress [6, 7]. This my be due to poor vsculrity of the ground substnce of musculoskeletl tissues precluding enzyme ccess. Enzyme replcement therpy (ERT) is used to tret ttenuted MPS I nd severe nd ttenuted MPS II. In ttenuted MPS I, recombinnt humn -L-iduronidse results in short- nd medium-term clinicl improvements [8]. Enzymes re unble to cross the blood brin brrier so provide no cognitive benefit in severe MPS I. Recombinnt humn iduronte-2-sulftse is beneficil in severe [9] nd ttenuted MPS II [20]. Although ERT cn improve joint rnge of motion, no improvement is seen in hip dysplsi or genu vlgum [2]. Improved life expectncy nd qulity of life, resulting from HSCT nd ERT, hve resulted in more ptients nd doctors considering surgicl intervention for genu vlgum. Surgicl correction of knee deformity using guided growth ws first reported using stples [22]. More recently, the use of eight-pltes hs been described [8] but timing, indictions nd recurrence rtes remin uncler. The ims of this retrospective observtionl study re three-fold. Firstly, to describe knee deformity in children of different ges with severe MPS I nd II. Secondly, to describe deformity progression in individul children, nd thirdly, to report the outcome of tretment with guided growth in subgroup of ptients who demonstrted progressive deformity. Mterils nd Methodology All ptients with MPS I or II, who were treted t our institution between Jnury 2004 nd December 204, with minimum of one full-length stnding leg X-ry were included in the study. X-rys were stndrdised with ptelle fcing forwrd, level pelvis nd mesurement bll on ech film. A totl of 29 children (58 legs) were included in the study 7 children with severe MPS I nd 2 children with severe MPS II. There were 0 mles nd 7 femles in the MPS I group. The MPS II group ws entirely mle. All MPS I ptients hd received HSCT (2/7 subsequently received ERT). All MPS II ptients were receiving ERT. Tretments were strted prior to rdiogrphic ssessment of knee lignment. The Picture Archiving nd Communiction System ws used to determine the lignment of ech knee by mesuring mechnicl xis devition (MAD). MAD ws clssified s pssing through one of four zones. A positive vlue indicted vlgus knee nd negtive vlue indicted vrus knee. Zones were clculted in reltion to the width of the tibil plteu (Fig. ). The source of knee deformity ws determined by mesuring the mechnicl lterl distl femorl ngle (mldfa) nd the medil proximl tibil ngle (MPTA). The men nd rnge of ech rdiogrphic mesure is reported for X-rys between the ges of 2 nd 9 yers for MPS I nd between the ges of 4 nd 3 yers for MPS II (or within 6 months of ech time point). No child with MPS I hd limb lignment X-ry performed under the ge Fig. Rdiogrph showing the zones of the knee. Zone 0 is verticl line through the centrl point of the tibil plteu (thick white line). Ech hlf of the tibil plteu is divided into two. Zone is locted next to the centrl line nd zone 2 is more peripherl. A verticl line is drwn on either side of the knee t distnce equl to the width of the tibil hemi-plteu. Zone 3 lies between the tibil plteu nd this line nd zone 4 lies outside this line. The mechnicl xis devition zones hve positive vlues in vlgus knee nd negtive vlues in vrus knee

3 J Child Orthop (205) 9: Tble Number nd timing of full-length leg X-rys used to ssess knee lignment over time MPS I MPS II Number of knees evluted 24 6 Men number of knee X-rys tken (rnge) 4.8 (3-2) 3.6 (3-5) Men ge t first X-ry (rnge) 6.9 yers ( ) 7.5 yers ( ) Men ge t finl X-ry (rnge) 0.0 yers ( ).2 yers ( ) Men time between first nd finl X-ry (rnge) 3. yers (.0 4.9) 3.7 yers (0.9 5.) of 2 yers nd no child with MPS II hd n X-ry performed under the ge of 4 yers. Corrective surgery ws performed t men ge of 9 yers in MPS I nd 3 yers in MPS II. Rdiogrphs fter the implementtion of guided growth techniques re not reported in this prt of the study s they would not be representtive of nturl progression. In totl, 67 rdiogrphs (34 knees) in children with MPS I nd 37 rdiogrphs (74 knees) in children with MPS II were evluted. To ssess disese progression in individul children, only those with minimum of 3 X-rys prior to ny surgicl intervention were included for nlysis. There were 2 children with MPS I (24 knees) nd 8 children with MPS II (6 knees). Detils of the number nd timing of X-rys re shown in Tble. Rdiogrphic findings on the initil X-ry were compred to those on the finl X-ry. To ssess the rte of disese progression, the chnge in rdiogrphic ppernce ws divided by the time tken for the chnge to occur. A totl of 0 children (7 with MPS I nd 3 with MPS II) were treted with guided growth using Orthofix eightpltes. Indictions for surgery included MAD through zone 3 or higher or MAD through zone 2 together with evidence of deformity progression. The origin of the knee deformity ws estblished from the mldfa nd MPTA. Eight-pltes were inserted into the proximl tibi nd/or the distl femur s pproprite. Rdiogrphic mesurements t the time of eight-plte insertion, t eight-plte removl nd t yer following eight-plte removl re reported. Mechnicl xis devition / Zone Mechnicl xis devition / Zone b Age / yers Age / yers Fig. 2 Mechnicl xis devition in children with MPS I t different ges. Grey dot represents the men vlue nd the blck line represents the rnge. b Mechnicl xis devition in children with MPS II t different ges. Grey dot represents the men vlue nd the blck line represents the rnge Results Knee lignment in children of different ges The MAD, mldfa nd MPTA were ssessed in 29 children (58 legs) t different ges. Results re shown in Figs. 2, 3 nd 4, respectively, highlighting the differences between MPS I nd II ptients. Deformity progression in individul children Deformity progression over time ws ssessed in 20 children (40 knees). Results re shown in Tble 2. In knees with progressive deteriortion in mechnicl xis devition, the men rte of chnge in MPS I ws 0.5 zones/yer (rnge ) nd in MPS II ws 0.59 zones/yer (rnge ). Results of tretment with guided growth A totl of 0 children (20 knees) were treted with guided growth. The pltes were removed in 6 cses (2 knees); detils re given in Tble 3. There ws correction of deformity to MAD zone, 0 or in ll cses. The men time pltes remined in situ ws.6 yers. Deformity recurred in 3 children (6 knees) following plte removl.

4 230 J Child Orthop (205) 9: mldfa/ b mldfa/ Correction ws mintined in one ptient (2 legs) who ws skeletlly mture t the time of plte removl. Detils of the 4 children (8 knees) where eight-pltes remined in situ re given in Tble 4. The MAD is showing improvement in ll cses. Discussion Age / yers Age / yers Fig. 3 Mechnicl lterl distl femorl ngle (mldfa) in children with MPS I t different ges. Grey dot represents the men vlue nd the blck line represents the rnge. The hevy horizontl line highlights the norml vlue of 88. b Mechnicl lterl distl femorl ngle (mldfa) in children with MPS II t different ges. Grey dot represents the men vlue nd the blck line represents the rnge. The hevy horizontl line represents the norml vlue of 88 Knee deformity is common in children with MPS types I nd II. Knee lignment in MPS hs previously been described using the tibio-femorl ngle only [8, 22]. Children with MPS hve high incidence of hip dysplsi [8] nd therefore norml tibio-femorl ngle my not correlte with norml mechnicl xis. It is for this reson tht MAD ws used in this study. In MPS I, grdul increse in the men MAD ws seen in children of incresing ge. This trend ws less cler in children with MPS II. All MPS I children [8 yers hd vlgus knee lignment. In MPS II children, 75 %[8 yers hd vlgus knee lignment, 2 % hd vrus lignment nd 4 % hd neutrl lignment. MPS I children tended to hve mmpta/ b mmpta/ Age / yers Age / yers Fig. 4 Medil proximl tibil ngle (MPTA) in children with MPS I t different ges. Grey dot represents the men vlue nd the blck line represents the rnge. The hevy horizontl line represents the norml vlue of 88. b Medil proximl tibil ngle (MPTA) in children with MPS II t different ges. Grey dot represents the men vlue nd the blck line represents the rnge. The hevy horizontl line represents the norml vlue of 88 Tble 2 Chnge in mechnicl xis devition in individul children with time Chnge in MAD with time MPS I MPS II Deteriortes 5/24 (63 %) 8/6 (50 %) Remins constnt 9/24 (37 %) 6/6 (38 %) Improves 0/24 (0 %) 2/6 (2 %) greter knee deformity thn MPS II children of the sme ge. No MPS II child hd MAD through zone 4, lthough seven MPS I children did. With incresing ge, there ws no chnge in the mldfa in children with MPS I nd MPS II. A vlgus distl femur (mldfa B 85 ) ws more common in MPS I nd vrus distl femur (mldfa C 9 ) ws more common in MPS II. In MPS I children of incresing ge, there ws stedy increse in the men MPTA. There ws no cler trend in MPS II. All MPS I children[8 yers hd vlgus proximl tibi (mmpta C 9 ). In MPS II children[8 yers, 69 %

5 J Child Orthop (205) 9: Tble 3 Detils of guided growth procedures performed on 6 children (2 knees) where the pltes hve been removed Child number Type of MPS Gender Side of opertion Bone primrily cusing deformity Age eight-plte(s) inserted/yers Age eight-plte(s) removed/yers Time eight-plte in situ/yers MAD Zone before eight-plte insertion MAD Zone fter eight-plte removl MAD Zone one yer fter removl I F Right Tibi/femur Left Tibi/femur I F Right Femur Left Femur I F Right Tibi/femur Left Tibi/femur II M Right Tibi Left Tibi I M Right Tibi Left Tibi II M Right Tibi Left Tibi Insufficient time elpsed to provide figures for ptients 4 nd 5 Tble 4 Detils of guided growth procedures performed on 4 children (8 knees) where the pltes remin in situ Child number Type of MPS Gender Side of opertion Bone primrily cusing deformity Age eight-plte(s) inserted/yers Time since eight-pltes inserted/yers MAD Zone before eight-plte insertion MAD Zone t present time with eight-pltes in-stu 7 I M Right Tibi Left Tibi I M Right Tibi Left Tibi I F Right Femur/tibi Left Femur/tibi II M Right Tibi Left Tibi hd vlgus proximl tibi nd 3 % hd neutrl lignment. No child of ny ge with MPS I or II hd vrus proximl tibi (mmpta B 85 ). In individul children, the MAD worsened over time in pproximtely two-thirds of MPS I knees nd hlf of MPS II knees. On verge, it took 2 yers for the MAD to progress one zone. In MPS I, the fstest deforming knee took yer to progress one MAD zone. In MPS II, the fstest deforming knee took \8 months to progress one MAD zone. Guided growth using eight-pltes dequtely corrected knee lignment in ll cses. Recurrence of deformity ws seen in three of four (75 %) cses t yer following plte removl. Correction ws mintined in cse. This ptient ws skeletlly mture t the time of eight-plte removl. X-rys of typicl MPS I ptient following eight-plte insertion nd removl re shown in Fig. 5. We believe there re 2 dvntges to treting skeletlly immture children with guided growth, despite deformity recurrence following plte removl. Firstly, deformity progression is delyed. The pltes remin in situ for men of.6 yers nd it tkes yer for deformity to recur following plte removl. Thus, there is no deformity progression for over 2 yers. In this time period, deformity progression of over one MAD zone (bsed on our results) would be expected if the pltes hd not been inserted. Secondly, deformity is not llowed to rech criticl level tht could limit function. The correltion between knee deformity nd function in children with MPS requires further reserch. Recurrent deformity cn be treted by reppliction of the guided growth principles. Knee deformity in children with MPS hs previously been reported. Stoop et l. [7] described genu vlgum in series of 3 knees in 3 children with MPS I. They reported

6 232 J Child Orthop (205) 9: Fig. 5 X-rys showing typicl improvement in knee lignment with insertion of eight-pltes nd recurrence of deformity following plte removl high MPTA in 2/3 knees. A similr result ws found in our series. Stoop et l. did not report overll knee lignment or the femorl contribution to knee deformity. They reported mximum MPTA vlue between the ges of 3 nd 5 yers. This differs from our study where the men MPTA continued to increse until t lest 9 yers of ge. Tretment with guided growth in MPS hs previously been reported. Tylor et l. [22] reported 5 ptients with MPS I treted with stpling of the medil tibil epiphysis. The tibio-femorl ngle corrected from men of 7 to 0. The contribution of the distl femur to the knee deformity nd recurrence rtes following stple removl re not reported. Odunusi et l. [8] described tretment with guided growth in 8 vlgus knees in children with MPS I using stples. There ws complete correction of deformity in 2 knees nd incomplete correction in 6 knees. Deformity recurred in 5 cses fter stple removl nd there ws incomplete follow-up in cse. There ws no recurrence in 2 knees. Both these ptients were ner skeletl mturity t the time of stple removl (ge 4 nd 5 yers, respectively). This is the sme s our study where there ws no recurrence in one ptient who hd reched skeletl mturity prior to plte removl. There re two possible strtegies for tretment with guided growth. The first strtegy involves performing surgery when knee lignment becomes uncceptble, e.g., when the MAD progresses to zone 3 on the ssumption tht gross deformity does lter git mechnics nd is ssocited with discomfort. Erly tretment would correct the MAD nd knee lignment would be mintined within specified limits to limit pin nd mintin function. A disdvntge is tht child my require two or three surgicl interventions during their childhood to chieve neutrl limb lignment t skeletl mturity. A second strtegy would be to dely tretment with guided growth until the child is nering skeletl mturity in n ttempt to chieve norml knee lignment t the time skeletl mturity is reched. An dvntge of this strtegy is tht it requires single opertion. A disdvntge is tht child my develop severe deformity tht limits function; correction of MAD in zone 4 my not occur so relibly s in younger child prticulrly s the rte of deformity correction vries between individuls, so it would be difficult to estimte the time of plte insertion. If pltes were inserted too erly they would need to be removed with the risk of deformity recurrence. If the pltes were inserted too lte there would be under-correction of the deformity. Our study hs severl strengths. It hs lrge study popultion for such rre condition, there re severl stnding long-leg X-rys for mny ptients llowing disese progression to be reported over time nd 3 importnt spects of knee lignment hve been reported (MAD, mldfa nd MPTA). This study lso hs weknesses. It ws performed retrospectively nd is bsed solely on rdiogrphic mesurements tht my not correlte to ptient symptoms. Rdiogrphs were tken t different ges nd t different time intervls. Deformity progression ws ssessed in individul knees over men time period of 3 yers. Studies with longer follow-up re necessry to ssess progression throughout childhood. For the tretment rm of this study, only 8 knees underwent -yer follow-up following plte removl, mking this cse series rther thn true study. Nevertheless, we hve shown tht guided growth hs the potentil to improve significnt deformity nd mintin it in the short term. Medicl tretments for MPS I nd MPS II [23, 24] hve improved life expectncy nd qulity of life, resulting in more ptients nd doctors considering guided growth to correct knee lignment. When considering surgery, it is

7 J Child Orthop (205) 9: importnt to tret the source of the deformity (tibi, femur or both). Surgery should only be considered if the deformity is sufficiently severe or shows evidence of progression. This study shows tht not ll deformities progress in the medium-term. Ptients should be wre of the high rte of deformity recurrence following plte removl nd the need for further surgery in the future. It remins to be seen whether guided growth tretments cn deliver stright leg t skeletl mturity in children with MPS I nd MPS II. Acknowledgements Neither uthor ws in receipt of ny funding. Conflict of interest D. M. Estwood nd E. Ashby declre tht they hve no conflict of interest. Ethicl pprovl This rticle does not contin ny studies with humn prticipnts or nimls performed by ny of the uthors. Informed consent All ptients undergoing surgicl procedures were subject to informed consent. 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