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Carpal height and postoperative strength after proximal row carpectomy or four-corner arthrodesis: Clinical, anatomical and biomechanical study
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ScienceDirect www.sciencedirect.com Hand Surgery and Rehabilitation 35 (2016) 100–106
Original article
Carpal height and postoperative strength after proximal row carpectomy or four-corner arthrodesis: Clinical, anatomical and biomechanical study Hauteur du carpe et force postopératoire après résection de la rangée proximale ou arthrodèse des quatre os médiaux avec scaphoïdectomie : étude clinique, anatomique et biomécanique Pascale Laronde a,*,b, Nicolas Christiaens a, Aurélien Aumar a,b, Christophe Chantelot a,c, Christian Fontaine a,b,d a Service d’orthopédie B, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France Laboratoire d’anatomie, faculté de médecine de Lille, 1, place de Verdun, 59045 Lille cedex, France c Service de traumatologie, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France d Laboratoire d’automatique, de mécanique et d’informatique industrielle et humaine LAMIH, université de Valenciennes et du Hainaut-Cambrésis, Le Mont Houy, 59313 Valenciennes cedex, France b
Received 2 September 2015; received in revised form 29 December 2015; accepted 10 January 2016 Available online 17 March 2016
Abstract Proximal row carpectomy (PRC) and four-corner arthrodesis (4CA) are the two most commonly performed surgical procedures to treat wrist arthritis. Postoperative strength is one of the criteria for choosing between the two techniques. Some authors believe that strength is correlated with residual carpal height. The goal of this study was to determine if postoperative carpal height was predictive of postoperative strength. This study consisted of two parts: a clinical evaluation of grip strength after 4CA or PRC; anatomical and radiological measurements of carpal height before and after 4CA or PRC. Grip strength was better preserved after PRC (87.5%) than after 4CA (76.1%), when expressed relative to the opposite hand (P = 0.053). There was a significant decrease in carpal height for the PRC group with a Youm’s index of 0.37 versus 0.50 for the 4CA group (P < 0.0001). Our clinical results and analysis of the literature indicate that 4CA is not superior to PRC when it comes to grip strength, whereas carpal height is significantly decreased after PRC. The decreased tendon excursion after PRC is balanced by an increase in joint stresses after 4CA. # 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved. Keywords: Four-corner arthrodesis; Proximal row carpectomy; Carpal height; Grip strength; Tendon excursion
Résumé Résection de la rangée proximale du carpe (RRPC) et arthrodèse des quatre os médiaux (A4O) avec scaphoïdectomie sont des interventions couramment pratiquées dans la prise en charge de l’arthrose de poignet. La force postopératoire est un critère de choix entre ces deux techniques. Pour certains, elle est corrélée à la hauteur résiduelle du carpe. L’objectif de l’étude était de déterminer si la hauteur du carpe après intervention était prédictive de la force postopératoire. Cette étude est composée de deux parties : un recueil clinique de la force de poigne après A4O ou RRPC ; une étude anatomique et radiologique mesurant la hauteur du carpe avant et après A4O ou RRPC. La force de poigne était mieux conservée après RRPC (87,5 %) qu’après A4O (76,1 %) comparativement au côté opposé ( p = 0,053). Il existait une diminution significative de la hauteur du carpe pour le groupe RRPC avec un indice de Youm à 0,37 contre 0,50 pour le groupe A4O ( p < 0,0001). Nos résultats cliniques et l’analyse de la littérature ne mettent pas en évidence de supériorité de l’A4O concernant la conservation de la force alors que la hauteur du carpe est diminuée de façon
* Corresponding author. Service d’orthopédie B, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France. E-mail address: [email protected] (P. Laronde). http://dx.doi.org/10.1016/j.hansur.2016.01.003 2468-1229/# 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved.
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significative après RRPC. La diminution de l’excursion tendineuse après RRPC est contrebalancée par l’augmentation des contraintes après A4O expliquant possiblement ces résultats. # 2016 SFCM. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Arthrodèse des quatre os ; Résection de la rangée proximale du carpe ; Hauteur du carpe ; Force de poigne ; Excursion tendineuse
1. Introduction Wrist arthritis mainly manifests itself as a consequence of posttraumatic conditions such as scapholunate advanced collapse (SLAC wrist) and scaphoid nonunion advanced collapse (SNAC wrist). The two main surgical techniques used for wrist arthritis are proximal row carpectomy (PRC) and four-corner arthrodesis with scaphoid excision (4CA). The patient, the condition’s severity and the surgeon’s preferences are taken into consideration when choosing between these two techniques [1–12]. Other than the extent of the contact area and the configuration of the joint surfaces [13–15], the primary difference between the two procedures in terms of the postoperative anatomy is the residual carpal height (CH) [9,10,16]. Reduced carpal height results in reduced strength [5,7–9,17], because there is less tension on the wrist and finger flexors and extensors [16]. While the possibility of maintaining postoperative strength comes into play when choosing between these two techniques, particularly for patients who perform manual work [7,8,18,19], there is no research showing that one technique is truly superior to the other [1,8,9,11,12,17,20]. Our study had two goals: compare the clinical outcomes of PRC and 4CA, particularly the grip strength, for patients operated in our surgery unit; study the link between carpal height, tendon excursion and strength through an anatomical study in which the preoperative and postoperative carpal height following 4CA is compared with that following PRC. 2. Material and methods 2.1. Comparison of clinical outcomes after PRC or 4CA The first part of the study was retrospective and included all the patients who underwent PRC or 4CA procedures in our surgery unit between 2004 and 2011, including those who had a history of surgery before the PRC. Patients who had a surgical revision after PRC or 4CA were excluded. The study consisted of two independent groups of patients; although they were not paired, they were comparable. The patients were informed about the study and gave their consent. In the clinical PRC group, 22 patients were reviewed (4 women, 18 men). The dominant hand had been operated on in 9 of 22 cases (41%). The PRC was performed because of SLAC wrist in 36% of cases (8/22), Kienböck’s disease in 36% (8/22), and SNAC wrist in 23% (5/22). The mean overall age was 44.9 years (22–72); the mean age was 38.4 years (24–50) in the Kienböck’s disease sub-group and 48.6 years (22–72) in the SNAC/SLAC wrist sub-group. The average follow-up was 50 months (21–77).
In the clinical 4CA group, 11 patients were reviewed (6 women, 5 men). The mean age of these patients was 54.5 years (37–64) and the mean follow-up was 27 months (11–55). The dominant hand had been operated on in 5 of 11 cases (46%). The 4CA was performed because of SLAC wrist in 64% of cases (7/11), and SNAC wrist in 36% (4/11). Screws (5/11), plates (4/11) or staples (3/11) had been used for the arthrodesis. The age difference between the two groups was statistically significant (P = 0.017), as was the sex ratio (P = 0.0413). In both groups, the grip strength was measured at the time of review in the operated and nonoperated hands. Strength testing was carried out using a BaselineTM dynamometer (0 to 90 kg) (AREX, Palaiseau, France) that was secured to a table. Patients were seated on an adjustable stool with their elbow flexed at 908; their arm was held against the chest with a soft, nonstretchy, horizontal strap. They performed three trials of grip strength with 10 seconds rest between trials. The best of the three trials was recorded. In addition, the joint range of motion was measured with a goniometer (flexion, extension, radial deviation, ulnar deviation, pronation and supination), and the Cooney score [21] and the PRWE (Patient-Rated Wrist Evaluation) [22] were calculated for patients in both groups. The thresholds for the Cooney score were: 0 to 60 (poor), 60 to 80 (average), 80 to 90 (good), 90 to 100 (excellent). The PRWE score ranges from 0 to 100 points, with 100 being the worst possible score. Standard A/P and lateral radiographs of the wrist were done with the wrist in neutral position. These were used to measure the CH between the lunate facet of the distal radius and the base of the third metacarpal, along with the length of the third metacarpal (M3). Youm’s index (CH/M3) was calculated [23,24]; this is a relative measurement of CH that has a normal value between 0.51 and 0.57 (Fig. 1). The mean and standard deviation values were calculated for each group. The non-parametric Wilcoxon test was used to compare paired data because the sample size was less than 30. Linear correlation coefficients were calculated using Spearman’s rho because the sample sizes were less than 30. The nonparametric Kruskal–Wallis test was used to compare unpaired data because the sample size was less than 30. Fisher’s exact test was used to compare the distribution of qualitative variables because of the small size of the 4CA group (n < 30). For each of the tests performed, the type I error was set at 0.05. 2.2. Comparison of preoperative and postoperative carpal height in cadaver wrists following PRC or 4CA The second part of the study was carried out on 20 pairs of upper limbs from 5 male and 15 female cadavers with no
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Fig. 2. Proximal row carpectomy (PRC) (a) and four-corner arthrodesis with scaphoid excision (4CA) (b).
Fig. 1. AP X-ray of the left wrist. Carpal height (CH): 35.2 mm; third metacarpal length (M3): 71.3 mm; carpal height ratio (CHR) based on Youm’s index: 0.49.
history of wrist surgery. The mean age was 79 years (50–100). Standard radiographs of the wrist were performed before and after the surgical procedure. The CH and Youm’s index were calculated from these radiographs. It was arbitrarily decided to perform PRC on the right wrists and 4CA on the left. Each wrist served as its own control (Fig. 2). The 4CA was carried out after decortication and exposure of subchondral bone; the bones were fixed with a 2-mm diameter cannulated compression screw (Small Bone Innovations Inc., Morrisville, PA, USA). Only the capitolunate and lunotriquetral joints were fused. Minimal decortication was carried out so that the fusion would
shorten the wrist as little as possible, thereby making it unnecessary to graft the interosseous spaces. In some of the wrists that underwent PRC, the postoperative radiographs revealed excessive space between the capitate head and the lunate fossa on the radius caused by the absence of muscle tone. We took new radiographs with the joint compressed to place the cartilage surfaces in contact, so as to not alter the results (Fig. 3). The quantitative variables were described using their mean and standard deviation values; the qualitative variables were described by their numbers and percentages. The differences in the radiological measurements of CH and M3 between the two groups before the surgery and the differences in preoperative and postoperative CH, M3 and Youm’s index between the two groups and within each group were calculated and compared using a linear mixed model to take into account the pairing between groups, and to adjust the measurements before the
Fig. 3. Left to right: AP X-ray of right wrist before proximal row carpectomy (a), after proximal row carpectomy without axial compression (b), after proximal row carpectomy with axial compression (c).
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surgery (the group was the fixed effect and the subjects were the variable effect). The threshold for significance of these tests was set at 5%. The statistical analysis was carried out using SAS software (version 9.3, SAS Institute Inc., Cary, NC, USA).
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shortening in the PRC group versus 3% in the 4CA group. The mean Youm’s index was 0.38 (0.31–0.43) in the PRC group versus 0.52 (0.44–0.60) in the 4CA group (P < 0.001). 4. Discussion
3. Results 3.1. Comparison between clinical PRC and 4CA groups 3.1.1. Strength The mean grip strength in the PRC group was 35 kg (22–51) in the operated hand versus 40 kg (12–62) in the nonoperated contralateral hand. These values did not differ between the Kienböck’s disease and SNAC/SLAC wrist sub-groups. These values meant that 87.5% of the strength had been recovered. The mean grip strength in the 4CA group was 51 kg (16–90) in the operated hand versus 67 kg (19–90) in the nonoperated, contralateral hand. These values meant that 76.1% of the strength had been recovered. The strength difference between the operated and nonoperated side was significant for both groups (P = 0.001). 3.1.2. Joint range of motion The mean flexion range was 438 [10–708] in the PRC group and 258 [0–528] in the 4CA group (P = 0.0002). The mean extension was 598 [10–908] in the PRC group and 248 [12–428] in the 4CA group (P < 0.0001). The mean radial deviation was 108 [0–158] in the PRC group and 138 [4–208] in the 4CA group (P < 0.0001). The mean ulnar deviation was 268 [5–408] in the PRC group and 228 [8–328] in the 4CA group (P = 0.0003). The mean pronation was 888 [55–908] in the PRC group and 858 [85–858] in the 4CA group (P = 0.5). The mean supination was 878 [50–908] in the PRC group and 858 [50–908] in the 4CA group (P = 0.6). 3.1.3. Clinical scores The Cooney score was 68.5 (25–100) in the PRC group and 63.6 (40–90) in the 4CA group (P = 0.3544). The PRWE score was 24.9 (1–67) in the PRC group and 44.6 (7–128) in the 4CA group (P = 0.1527). 3.1.4. Carpal height Youm’s index was 0.37 (0.32–0.41) in the PRC group and 0.50 (0.43–0.59) in the 4CA group (P < 0.0001). 3.2. Comparison of pre- and postoperative carpal height in cadaver wrists following PRC or 4CA Before any of the surgical procedures were performed in the 20 right wrists, the CH was 35.2 mm (30.8–40.2 mm) and Youm’s index was 0.53 (0.46–0.58). In the 20 left wrists, the CH was 35.8 mm (32.1–39.7 mm) and Youm’s index was 0.54 (0.48–0.63). There were no significant preoperative differences between these two groups. After the surgical procedures, the mean CH was 24.9 mm (21.6–28.3 mm) in the PRC group versus 34.7 mm (30.5– 43.0 mm) in the 4CA group. This was equal to 29% carpal
The first part of our study involved a comparison of grip strength after PRC or 4CA. The grip strength in the nonoperated hand was significantly different between the two clinical groups (P = 0.0001). The difference was +67.5% in the 4CA group, despite this group being 54.5% female, versus 18.2% in the PRC group. This was an unusual finding [25] that was likely due to a difference in the dynamometer’s calibration, which had been used over the span of two years. This led us to use relative values instead of absolute values when comparing the two groups. In the clinical PRC group, 87.5% of the grip strength was maintained versus 76.1% in the 4CA group. Better grip strength was maintained after PRC than 4CA. CH was significantly different between the groups: Youm’s index of 0.37 for the PRC and 0.50 for the 4CA group. While the carpal height was better preserved with 4CA procedure, the grip strength was better with the PRC procedure. Unlike other authors, we found no statistical relationship between CH and postoperative grip strength [8]. This could be due, in part, to significant differences in age and sex distribution between the two groups. It could also be due to the inclusion of patients with Kienböck’s disease, even if there was no significant difference in terms of strength between the Kienböck’s disease and SNAC/SLAC wrist sub-groups. Although it was not the primary objective of our work, we performed a more in-depth analysis of the clinical groups. The Cooney and PRWE scores were better after PRC than 4CA, but not significantly. Range of motion was also better in the PRC patients: the mean flexion–extension range was 1028 in the PRC group versus 498 in the 4CA group, which is nearly double. These results are consistent with published data [1,8,18]. There were no postsurgical complications after PRC. In the 4CA group, two patients had signs of nonunion at the review and one had a broken screw. When the patients initially excluded because of complete wrist fusion after PRC (4 patients) or 4CA (1 patient) are included in the analysis, the complication rate was 33% (4/12) for the 4CA group versus 15% (4/26) for the PRC group. This suggests that a selection bias is present: the four PRC cases and one 4CA case that were excluded reduced the number of failures. Another bias was the difference in the length of follow-up at review: 50 months for the PRC group versus 27 months for the 4CA group. However, since the outcomes of these types of procedures are considered stable after 2 years, these groups were comparable. In terms of indications for surgery, other than Kienböck’s disease being an indication only for PRC, they were the same for both groups: 2/ 3 SNAC wrist and 1/3 SLAC wrist. The second part of the study sought to explore the link between CH, tendon excursion and grip strength using cadavers. While the results were as expected, our anatomical and radiographic study provided us with information that can be used to infer the consequences of each procedure on tendon
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P. Laronde et al. / Hand Surgery and Rehabilitation 35 (2016) 100–106 Table 1 Normal tendon excursion (Boyes [29]) and consequences on wrist and finger movements of reducing carpal height by 1 cm for proximal row carpectomy (PRC), 1 mm for four-corner arthrodesis (4CA). Muscle
Normal excursion Boyes [26]
Reduction in excursion after PRC (%)
Reduction in excursion after 4CA (%)
ECRB ECRL ECU FCU FCR
3.6 cm 3.7 cm 3.3 cm 3.3 cm 4.0 cm
27.8 27 30 30 25
2.8 2.7 3.0 3.0 2.5
ECRB: extensor carpi radialis brevis; ECRL: extensor carpi radialis longus; ECU: extensor carpi ulnaris; FCU: flexor carpi ulnaris; FCR: flexor carpi radialis.
Fig. 4. Kienböck’s disease before (a) and after (b) proximal row carpectomy.
excursion and postoperative strength. We were able to obtain statistically significant results because the two groups in the anatomical study were initially similar. In the 4CA technique first described by Watson et al. [26], fixation of the arthrodesis, followed by decortication and filling of the resulting defects with bone graft were intended to maintain the CH. We decided to perform minimal decortication of the bone surfaces so that bone grafting would not be necessary, thereby keeping the CH as close as possible to that obtained using Watson’s technique. The resulting loss in CH was negligible (3%). The postoperative CH was statistically different between the two groups, and corresponded generally to the lunate’s height [16,27]. This outcome is the maximum height a surgeon can expect after 4CA in minimally deformed wrists, with little decortication and complete reduction of the lunate and triquetrum on the capitate and hamate. But in reality, the CH is often slightly less, as we found in our clinical study: 0.50 vs 0.52. In cases of severe joint destruction, the preoperative CH is often already reduced. This was the case for two pathological wrists in our study (stage IIIB Kienböck disease according to Lichtman’s classification [28] and lunotriquetral instability): the difference in preoperative CH between the left and right wrists was greater than 3 mm, while the difference in the postoperative CH was less than the mean value (Fig. 4). The excess space between the capitate and lunate fossa of the radius, observed after PRC (Fig. 3), fully illustrates the principle of loss of tendon excursion. Tendon excursion can be defined as a length reserve for tendon motion during flexion and extension movements. Boyes [29] measured tendon excursion for wrist and finger tendons (Table 1). The theoretical consequence of CH reduction on tendon excursion and strength can be calculated for the PRC and 4CA procedures. PRC reduces tendon excursion of the wrist motor muscles by 25– 30%, versus only 2.5–3% for 4CA (Table 1), which is 10 times less. This reduction in tendon excursion is proportional to the reduction in CH (Table 1). According to the length–tension
diagram for a muscle-tendon unit [30,31], maximum muscle power is developed in the middle two-thirds of the tendon’s excursion. Reducing tendon excursion by 25–30% should inevitably reduce the resulting muscle power to a greater degree for PRC than 4CA. This has already been shown for pathologies affecting the radius, scaphoid [32–34], metacarpals [35] and humerus [36]. For example, the extension strength of the triceps is reduced 17% for 1 cm of humerus shortening, 40% for 2 cm and 63% for 3 cm [36]. What are the practical clinical consequences for PRC? The loss of CH results in an imbalance between skeleton length and tendon length. A portion of the tension developed by the muscle-tendon units in the wrist is used to hold the newly formed radiocapitate joint together. As a consequence, this muscle tension is no longer available to move the fingers; additional muscle activation is needed to restore full flexion and extension movements. Since these muscles are recruited beyond the optimal middle two-thirds of the tension-length curve and they cannot contract beyond a threshold, the result is a loss of strength [32–35,37]. Since the 4CA procedure preserves the CH, the length of the tendons that cross the wrist is unchanged, thereby reducing the possibility of muscle weakness [38]. Despite this, there is no published data showing strength to be superior with 4CA than with PRC [5,9,12,17,20], as we found in this clinical study. There are several possible explanations: first, the muscles adapt to the decreased distance between the proximal and distal attachments of the muscle-tendon unit following PRC. The muscle body gradually remodels itself to return to its optimal length on the length–tension curve, which allows the strength to recover in the PRC group [39]; however, this is no experimental proof of this. Another factor may be the increased joint stresses due to changes in the joint spaces. In a normal wrist, the movements mainly occur at the radiocarpal and mid-carpal joints. When the mid-carpal joint is fused after the 4CA procedure but the CH is maintained, the tension in the muscletendon units can increase. This is due to an increased moment arm on the carpus, which no longer bends at the mid-carpal joint. Conversely, PRC reduces CH and places noncongruent joints surfaces in contact, thereby reducing the joint stresses. This has been confirmed by DeBottis et al. who showed that
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more strength was needed to carry out the same movements after 4CA than in normal wrists. When compared to normal wrists, PRC requires less strength for the same movements [38]. These results were significant and demonstrated for the extensor carpi ulnaris, extensor carpi radialis brevis and longus, along with the flexor carpi ulnaris. The expected loss of strength after PRC due to reduced tendon excursion seems to be partially compensated by the reduction in strength needed to carry out movements [38]. This could explain the absence of significant differences in strength between PRC and 4CA procedures in most studies, including ours. It appears that the CH is not a major predictor for postoperative strength after PRC or 4CA. The debate between PRC and 4CA continues [1,8,10,11]. Advocates of 4CA believe that preserving the CH ensures the best possible postoperative strength, despite longer postoperative recovery and more postoperative complications (infection, nonunion, broken hardware) [3,5,9,12,17]. Proponents of PRC emphasize the relative simplicity of the procedure and the lower complication rate. Our study found PRC to be superior to 4CA in terms of postoperative strength, range of motion and clinical scores. It also calls into question the relationship between CH and postoperative strength. For common indications such as stage I and II SNAC and SLAC wrists, we advocate performing PRC based on the results of published studies and our own clinical study. If PRC is contraindicated, such as in cases of stage III SNAC and SLAC wrists, 4CA is still the best solution [1,2]. 5. Conclusion Neither our study nor other published studies provide evidence that 4CA is better than PRC. On the contrary, PRC leads to better outcomes relative to strength, joint range of motion and clinical scores. Our findings suggest that postoperative strength is not a function of residual carpal height alone. This can be explained by muscle and joint biomechanics: the reduction in tendon excursion after PRC is counterbalanced by the greater joint stresses after 4CA. Disclosure of interest Christian Fontaine: clinical trials: as co-investigator, secondary experimenter, collaborator in the study for Hospital and Healthcare Consulting. Conferences: invitations as contributor for Allergan, Baxter, IPSEN and MERZ. He has no other competing interest to disclose. Christophe Chantelot: clinical trials: acting as principal investigator, coordinator or main experimenter for Howmedica (Guepar) and Aston Medical Evolutive. Pascale Laronde, Nicolas Christiaens and Aurélien Aumar declare that they have no competing interest. Acknowledgements Thank you to Dr. Emmanuel Camus for his insights, Drs. Varenka Baratinski and Arthur Lasnier for their work on
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pronation and supination forces, and Maurice Demeulaere, anatomy laboratory technician for his help in preparing the cadavers. References [1] Tomaino MM, Miller RJ, Cole I, Burton RI. Scapholunate advanced collapse wrist: proximal row carpectomy or limited wrist arthrodesis with scaphoid excision? J Hand Surg Am 1994;19:134–42. [2] Wyrick JD. Proximal row carpectomy and intercarpal arthrodesis for the management of wrist arthritis. J Am Acad Orthop Surg 2003;11(4)277–81. [3] Sauerbier M, Bickert B, Tränkle M, Kluge S, Pelzer M, Germann G. Surgical treatment possibilities of advanced carpal collapse (SNAC/SLAC wrist). Unfallchirurg 2000;103:564–71. [4] Krimmer H, Krapohl B, Sauerbier M, Hahn P. Post-traumatic carpal collapse (SLAC- and SNAC-wrist) – stage classification and therapeutic possibilities. Handchir Mikrochir Plast Chir 1997;29:228–33. [5] Wyrick 1 JD, Stern PJ, Kiefhaber TR. Motion-preserving procedures in the treatment of scapholunate advanced collapse wrist: proximal row carpectomy versus four-corner arthrodesis. J Hand Surg Am 1995;20:965–70. [6] Le Nen D, Richou J, Simon E, Le Bourg M, Nabil N, de Bodman C, et al. The arthritic wrist. I-the degenerative wrist: surgical treatment approaches. Orthop Traumatol Surg Res 2011;97(4)S31–6. [7] Laulan J, Bacle G, de Bodman C, Najihi N, Richou J, Simon E, et al. The arthritic wrist. II-the degenerative wrist: indications for different surgical treatments. Orthop Traumatol Surg Res 2011;97(4)S37–41. [8] Dacho AK, Baumeister S, Germann G, Sauerbier M. Comparison of proximal row carpectomy and midcarpal arthrodesis for the treatment of scaphoid nonunion advanced collapse (SNAC-wrist) and scapholunate advanced collapse SLAC-wrist in stage II. J Plast Reconstr Aesthet Surg 2008;61:1210–8. [9] Cohen MS, Kozin SH. Degenerative arthritis of the wrist: proximal row carpectomy versus scaphoid excision and four-corner arthrodesis. J Hand Surg Am 2001;26:94–104. [10] Wall LB, Stern PJ. Proximal row carpectomy. Hand Clin 2013;29:69–78. [11] Lukas B, Herter F, Englert A, Bäcker K. The treatment of carpal collapse: proximal row carpectomy or limited midcarpal arthrodesis? A comparative study. Handchir Mikrochir Plast Chir 2003;35:304–9. [12] Vanhove W, De Vil J, Van Seymortier P, Boone B, Verdonk R. Proximal row carpectomy versus four-corner arthrodesis as a treatment for SLAC (scapholunate advanced collapse) wrist. J Hand Surg Am 2008;33: 118–25. [13] Hogan CJ, McKay PL, Degnan GG. Changes in radiocarpal loading characteristics after proximal row carpectomy. J Hand Surg Am 2004;29: 1109–13. [14] Tang P, Gauvin J, Muriuki M, Pfaeffle JH, Imbriglia JE, Goitz RJ. Comparison of the ‘‘contact biomechanics’’ of the intact and proximal row carpectomy wrist. J Hand Surg Am 2009;34:660–70. [15] Zhu YL, Xu YQ, Ding J, Li J, Chen B, Ouyang YF. Biomechanics of the wrist after proximal row carpectomy in cadavers. J Hand Surg Eur 2010;35:43–5. [16] Richou J, Chuinard C, Moineau G, Hanouz N, Hu W, Le Nen D. Proximal row carpectomy: long-term results. Chir Main 2010;29:10–5. [17] Mulford JS, Ceulemans LJ, Nam D, Axelrod TS. Proximal row carpectomy vs. four corner fusion for scapholunate (SLAC) or scaphoid nonunion advanced collapse (SNAC) wrists: a systematic review of outcomes. J Hand Surg Eur Vol 2009;34:256–63. [18] Wall LB, Didonna ML, Kiefhaber TR, Stern PJ. Proximal row carpectomy: minimum 20-year follow-up. J Hand Surg Am 2013;38:1498–504. [19] Baumeister S, Germann G, Dragu A, Tränkle M, Sauerbier M. Functional results after proximal row carpectomy (PRC) in patients with SNAC-/ SLAC-wrist stage II. Handchir Mikrochir Plast Chir 2005;37:106–12. [20] Nakamura R, Horii E, Watanabe K, Nakao E, Kato H, Tsunoda K. Proximal row carpectomy versus limited wrist arthrodesis for advanced Kienböck’s disease. J Hand Surg Br 1998;26:741–5. [21] Amadio PC, Berquist TH, Smith DK, Ilstrup DM, Cooney WP, Linscheid RL. Scaphoid malunion. J Hand Surg Am 1999;14:679–87.
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[22] MacDermid JC. Development of a scale for patient rating of wrist pain and disability. J Hand Ther 1996;9:178–83. [23] Youm Y, McMurtry RY, Flatt AE, Gillespie TE. Kinematics of the wrist. II. Clinical applications. J Bone Joint Surg Am 1978;60:955–61. [24] Gilula LA, Mann FA, Dobyns JH, Yin Y. Wrist terminology as defined by the international wrist investigators’ workshop. J Bone Joint Surg Am 2002;84(1)1–73. [25] Dodds RM, Syddall HE, Cooper R, Benzeval M, Deary IJ, et al. Grip strength across the life course: normative data from twelve British studies. J Epidemiol Community Health 2014;68:1108. [26] Watson HK, Goodman ML, Johnson TR. Limited wrist arthrodesis. Part II: Intercarpal and radiocarpal combinations. J Hand Surg Am 1981;6: 223–33. [27] Lecomte F, Wavreille G, Limousin M, Strouk G, Fontaine C, Chantelot C. Proximal row carpectomy: 25 cases. Rev Chir Orthop Reparatrice Appar Mot 2007;93:444–54. [28] Lichtman DM, Degnan GG. Staging and its use in the determination of treatment modalities for Kienböck’s disease. Hand Clin 1993;9:409–16. [29] Boyes JH. Tendons transfers for radial palsy. Bull Hosp Joint Dis 1960;21:97. [30] Elftman H. Biomechanics of muscle with particular application to studies of gait. J Bone Joint Surg Am 1966;48:363–77. [31] Lieber 1 RL, Fridén J. Musculoskeletal balance of the human wrist elucidated using intraoperative laser diffraction. J Electromyogr Kinesiol 1998;8:93–100.
[32] Tang JB, Ryu J, Kish V, Wearden S. Effect of radial shortening on muscle length and moment arms of the wrist flexors and extensors. J Orthop Res 1997;15:324–30. [33] Tang JB, Ruy J, Omokawa S, Han J, Kish V. Biomechanical evaluation of wrist motor tendons after fractures of the distal radius. J Hand Surg Am 1999;24:121–32. [34] Tang JB, Ryu J, Han JS, Omokawa S, Kish V, Wearden S. Biomechanical changes of the wrist flexor and extensor tendons following loss of scaphoid integrity. J Orthop Res 1997;15:69–75. [35] Meunier MJ, Hentzen E, Ryan M, Shin AY, Lieber RL. Predicted effects of metacarpal shortening on interosseous muscle function. J Hand Surg Am 2004;29:689–93. [36] Hughes RE, Schneeberger AG, An KN, Morrey BF, O’Driscoll SW. Reduction of triceps muscle force after shortening of the distal humerus: a computational model. J Shoulder Elbow Surg 1997;6:444–8. [37] Strauch RJ, Rosenwasser MP, Lunt JG. Metacarpal shaft fractures: the effect of shortening on the extensor tendon mechanism. J Hand Surg Am 1998;23:519–23. [38] Debottis DP, Werner FW, Sutton LG, Harley BJ. 4-corner arthrodesis and proximal row carpectomy: a biomechanical comparison of wrist motion and tendon forces. J Hand Surg Am 2013;38:893–8. [39] Váczi M, Nagy SA, Ko˝szegi T, Ambrus M, Bogner P, Perlaki G, et al. Mechanical, hormonal, and hypertrophic adaptations to 10 weeks of eccentric and stretch-shortening cycle exercise training in old males. Exp Gerontol 2014;58:69–77.
ScienceDirect www.sciencedirect.com Hand Surgery and Rehabilitation 35 (2016) 100–106
Original article
Carpal height and postoperative strength after proximal row carpectomy or four-corner arthrodesis: Clinical, anatomical and biomechanical study Hauteur du carpe et force postopératoire après résection de la rangée proximale ou arthrodèse des quatre os médiaux avec scaphoïdectomie : étude clinique, anatomique et biomécanique Pascale Laronde a,*,b, Nicolas Christiaens a, Aurélien Aumar a,b, Christophe Chantelot a,c, Christian Fontaine a,b,d a Service d’orthopédie B, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France Laboratoire d’anatomie, faculté de médecine de Lille, 1, place de Verdun, 59045 Lille cedex, France c Service de traumatologie, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France d Laboratoire d’automatique, de mécanique et d’informatique industrielle et humaine LAMIH, université de Valenciennes et du Hainaut-Cambrésis, Le Mont Houy, 59313 Valenciennes cedex, France b
Received 2 September 2015; received in revised form 29 December 2015; accepted 10 January 2016 Available online 17 March 2016
Abstract Proximal row carpectomy (PRC) and four-corner arthrodesis (4CA) are the two most commonly performed surgical procedures to treat wrist arthritis. Postoperative strength is one of the criteria for choosing between the two techniques. Some authors believe that strength is correlated with residual carpal height. The goal of this study was to determine if postoperative carpal height was predictive of postoperative strength. This study consisted of two parts: a clinical evaluation of grip strength after 4CA or PRC; anatomical and radiological measurements of carpal height before and after 4CA or PRC. Grip strength was better preserved after PRC (87.5%) than after 4CA (76.1%), when expressed relative to the opposite hand (P = 0.053). There was a significant decrease in carpal height for the PRC group with a Youm’s index of 0.37 versus 0.50 for the 4CA group (P < 0.0001). Our clinical results and analysis of the literature indicate that 4CA is not superior to PRC when it comes to grip strength, whereas carpal height is significantly decreased after PRC. The decreased tendon excursion after PRC is balanced by an increase in joint stresses after 4CA. # 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved. Keywords: Four-corner arthrodesis; Proximal row carpectomy; Carpal height; Grip strength; Tendon excursion
Résumé Résection de la rangée proximale du carpe (RRPC) et arthrodèse des quatre os médiaux (A4O) avec scaphoïdectomie sont des interventions couramment pratiquées dans la prise en charge de l’arthrose de poignet. La force postopératoire est un critère de choix entre ces deux techniques. Pour certains, elle est corrélée à la hauteur résiduelle du carpe. L’objectif de l’étude était de déterminer si la hauteur du carpe après intervention était prédictive de la force postopératoire. Cette étude est composée de deux parties : un recueil clinique de la force de poigne après A4O ou RRPC ; une étude anatomique et radiologique mesurant la hauteur du carpe avant et après A4O ou RRPC. La force de poigne était mieux conservée après RRPC (87,5 %) qu’après A4O (76,1 %) comparativement au côté opposé ( p = 0,053). Il existait une diminution significative de la hauteur du carpe pour le groupe RRPC avec un indice de Youm à 0,37 contre 0,50 pour le groupe A4O ( p < 0,0001). Nos résultats cliniques et l’analyse de la littérature ne mettent pas en évidence de supériorité de l’A4O concernant la conservation de la force alors que la hauteur du carpe est diminuée de façon
* Corresponding author. Service d’orthopédie B, hôpital Roger-Salengro, rue Emile-Laine, 59037 Lille, France. E-mail address: [email protected] (P. Laronde). http://dx.doi.org/10.1016/j.hansur.2016.01.003 2468-1229/# 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved.
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significative après RRPC. La diminution de l’excursion tendineuse après RRPC est contrebalancée par l’augmentation des contraintes après A4O expliquant possiblement ces résultats. # 2016 SFCM. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Arthrodèse des quatre os ; Résection de la rangée proximale du carpe ; Hauteur du carpe ; Force de poigne ; Excursion tendineuse
1. Introduction Wrist arthritis mainly manifests itself as a consequence of posttraumatic conditions such as scapholunate advanced collapse (SLAC wrist) and scaphoid nonunion advanced collapse (SNAC wrist). The two main surgical techniques used for wrist arthritis are proximal row carpectomy (PRC) and four-corner arthrodesis with scaphoid excision (4CA). The patient, the condition’s severity and the surgeon’s preferences are taken into consideration when choosing between these two techniques [1–12]. Other than the extent of the contact area and the configuration of the joint surfaces [13–15], the primary difference between the two procedures in terms of the postoperative anatomy is the residual carpal height (CH) [9,10,16]. Reduced carpal height results in reduced strength [5,7–9,17], because there is less tension on the wrist and finger flexors and extensors [16]. While the possibility of maintaining postoperative strength comes into play when choosing between these two techniques, particularly for patients who perform manual work [7,8,18,19], there is no research showing that one technique is truly superior to the other [1,8,9,11,12,17,20]. Our study had two goals: compare the clinical outcomes of PRC and 4CA, particularly the grip strength, for patients operated in our surgery unit; study the link between carpal height, tendon excursion and strength through an anatomical study in which the preoperative and postoperative carpal height following 4CA is compared with that following PRC. 2. Material and methods 2.1. Comparison of clinical outcomes after PRC or 4CA The first part of the study was retrospective and included all the patients who underwent PRC or 4CA procedures in our surgery unit between 2004 and 2011, including those who had a history of surgery before the PRC. Patients who had a surgical revision after PRC or 4CA were excluded. The study consisted of two independent groups of patients; although they were not paired, they were comparable. The patients were informed about the study and gave their consent. In the clinical PRC group, 22 patients were reviewed (4 women, 18 men). The dominant hand had been operated on in 9 of 22 cases (41%). The PRC was performed because of SLAC wrist in 36% of cases (8/22), Kienböck’s disease in 36% (8/22), and SNAC wrist in 23% (5/22). The mean overall age was 44.9 years (22–72); the mean age was 38.4 years (24–50) in the Kienböck’s disease sub-group and 48.6 years (22–72) in the SNAC/SLAC wrist sub-group. The average follow-up was 50 months (21–77).
In the clinical 4CA group, 11 patients were reviewed (6 women, 5 men). The mean age of these patients was 54.5 years (37–64) and the mean follow-up was 27 months (11–55). The dominant hand had been operated on in 5 of 11 cases (46%). The 4CA was performed because of SLAC wrist in 64% of cases (7/11), and SNAC wrist in 36% (4/11). Screws (5/11), plates (4/11) or staples (3/11) had been used for the arthrodesis. The age difference between the two groups was statistically significant (P = 0.017), as was the sex ratio (P = 0.0413). In both groups, the grip strength was measured at the time of review in the operated and nonoperated hands. Strength testing was carried out using a BaselineTM dynamometer (0 to 90 kg) (AREX, Palaiseau, France) that was secured to a table. Patients were seated on an adjustable stool with their elbow flexed at 908; their arm was held against the chest with a soft, nonstretchy, horizontal strap. They performed three trials of grip strength with 10 seconds rest between trials. The best of the three trials was recorded. In addition, the joint range of motion was measured with a goniometer (flexion, extension, radial deviation, ulnar deviation, pronation and supination), and the Cooney score [21] and the PRWE (Patient-Rated Wrist Evaluation) [22] were calculated for patients in both groups. The thresholds for the Cooney score were: 0 to 60 (poor), 60 to 80 (average), 80 to 90 (good), 90 to 100 (excellent). The PRWE score ranges from 0 to 100 points, with 100 being the worst possible score. Standard A/P and lateral radiographs of the wrist were done with the wrist in neutral position. These were used to measure the CH between the lunate facet of the distal radius and the base of the third metacarpal, along with the length of the third metacarpal (M3). Youm’s index (CH/M3) was calculated [23,24]; this is a relative measurement of CH that has a normal value between 0.51 and 0.57 (Fig. 1). The mean and standard deviation values were calculated for each group. The non-parametric Wilcoxon test was used to compare paired data because the sample size was less than 30. Linear correlation coefficients were calculated using Spearman’s rho because the sample sizes were less than 30. The nonparametric Kruskal–Wallis test was used to compare unpaired data because the sample size was less than 30. Fisher’s exact test was used to compare the distribution of qualitative variables because of the small size of the 4CA group (n < 30). For each of the tests performed, the type I error was set at 0.05. 2.2. Comparison of preoperative and postoperative carpal height in cadaver wrists following PRC or 4CA The second part of the study was carried out on 20 pairs of upper limbs from 5 male and 15 female cadavers with no
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Fig. 2. Proximal row carpectomy (PRC) (a) and four-corner arthrodesis with scaphoid excision (4CA) (b).
Fig. 1. AP X-ray of the left wrist. Carpal height (CH): 35.2 mm; third metacarpal length (M3): 71.3 mm; carpal height ratio (CHR) based on Youm’s index: 0.49.
history of wrist surgery. The mean age was 79 years (50–100). Standard radiographs of the wrist were performed before and after the surgical procedure. The CH and Youm’s index were calculated from these radiographs. It was arbitrarily decided to perform PRC on the right wrists and 4CA on the left. Each wrist served as its own control (Fig. 2). The 4CA was carried out after decortication and exposure of subchondral bone; the bones were fixed with a 2-mm diameter cannulated compression screw (Small Bone Innovations Inc., Morrisville, PA, USA). Only the capitolunate and lunotriquetral joints were fused. Minimal decortication was carried out so that the fusion would
shorten the wrist as little as possible, thereby making it unnecessary to graft the interosseous spaces. In some of the wrists that underwent PRC, the postoperative radiographs revealed excessive space between the capitate head and the lunate fossa on the radius caused by the absence of muscle tone. We took new radiographs with the joint compressed to place the cartilage surfaces in contact, so as to not alter the results (Fig. 3). The quantitative variables were described using their mean and standard deviation values; the qualitative variables were described by their numbers and percentages. The differences in the radiological measurements of CH and M3 between the two groups before the surgery and the differences in preoperative and postoperative CH, M3 and Youm’s index between the two groups and within each group were calculated and compared using a linear mixed model to take into account the pairing between groups, and to adjust the measurements before the
Fig. 3. Left to right: AP X-ray of right wrist before proximal row carpectomy (a), after proximal row carpectomy without axial compression (b), after proximal row carpectomy with axial compression (c).
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surgery (the group was the fixed effect and the subjects were the variable effect). The threshold for significance of these tests was set at 5%. The statistical analysis was carried out using SAS software (version 9.3, SAS Institute Inc., Cary, NC, USA).
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shortening in the PRC group versus 3% in the 4CA group. The mean Youm’s index was 0.38 (0.31–0.43) in the PRC group versus 0.52 (0.44–0.60) in the 4CA group (P < 0.001). 4. Discussion
3. Results 3.1. Comparison between clinical PRC and 4CA groups 3.1.1. Strength The mean grip strength in the PRC group was 35 kg (22–51) in the operated hand versus 40 kg (12–62) in the nonoperated contralateral hand. These values did not differ between the Kienböck’s disease and SNAC/SLAC wrist sub-groups. These values meant that 87.5% of the strength had been recovered. The mean grip strength in the 4CA group was 51 kg (16–90) in the operated hand versus 67 kg (19–90) in the nonoperated, contralateral hand. These values meant that 76.1% of the strength had been recovered. The strength difference between the operated and nonoperated side was significant for both groups (P = 0.001). 3.1.2. Joint range of motion The mean flexion range was 438 [10–708] in the PRC group and 258 [0–528] in the 4CA group (P = 0.0002). The mean extension was 598 [10–908] in the PRC group and 248 [12–428] in the 4CA group (P < 0.0001). The mean radial deviation was 108 [0–158] in the PRC group and 138 [4–208] in the 4CA group (P < 0.0001). The mean ulnar deviation was 268 [5–408] in the PRC group and 228 [8–328] in the 4CA group (P = 0.0003). The mean pronation was 888 [55–908] in the PRC group and 858 [85–858] in the 4CA group (P = 0.5). The mean supination was 878 [50–908] in the PRC group and 858 [50–908] in the 4CA group (P = 0.6). 3.1.3. Clinical scores The Cooney score was 68.5 (25–100) in the PRC group and 63.6 (40–90) in the 4CA group (P = 0.3544). The PRWE score was 24.9 (1–67) in the PRC group and 44.6 (7–128) in the 4CA group (P = 0.1527). 3.1.4. Carpal height Youm’s index was 0.37 (0.32–0.41) in the PRC group and 0.50 (0.43–0.59) in the 4CA group (P < 0.0001). 3.2. Comparison of pre- and postoperative carpal height in cadaver wrists following PRC or 4CA Before any of the surgical procedures were performed in the 20 right wrists, the CH was 35.2 mm (30.8–40.2 mm) and Youm’s index was 0.53 (0.46–0.58). In the 20 left wrists, the CH was 35.8 mm (32.1–39.7 mm) and Youm’s index was 0.54 (0.48–0.63). There were no significant preoperative differences between these two groups. After the surgical procedures, the mean CH was 24.9 mm (21.6–28.3 mm) in the PRC group versus 34.7 mm (30.5– 43.0 mm) in the 4CA group. This was equal to 29% carpal
The first part of our study involved a comparison of grip strength after PRC or 4CA. The grip strength in the nonoperated hand was significantly different between the two clinical groups (P = 0.0001). The difference was +67.5% in the 4CA group, despite this group being 54.5% female, versus 18.2% in the PRC group. This was an unusual finding [25] that was likely due to a difference in the dynamometer’s calibration, which had been used over the span of two years. This led us to use relative values instead of absolute values when comparing the two groups. In the clinical PRC group, 87.5% of the grip strength was maintained versus 76.1% in the 4CA group. Better grip strength was maintained after PRC than 4CA. CH was significantly different between the groups: Youm’s index of 0.37 for the PRC and 0.50 for the 4CA group. While the carpal height was better preserved with 4CA procedure, the grip strength was better with the PRC procedure. Unlike other authors, we found no statistical relationship between CH and postoperative grip strength [8]. This could be due, in part, to significant differences in age and sex distribution between the two groups. It could also be due to the inclusion of patients with Kienböck’s disease, even if there was no significant difference in terms of strength between the Kienböck’s disease and SNAC/SLAC wrist sub-groups. Although it was not the primary objective of our work, we performed a more in-depth analysis of the clinical groups. The Cooney and PRWE scores were better after PRC than 4CA, but not significantly. Range of motion was also better in the PRC patients: the mean flexion–extension range was 1028 in the PRC group versus 498 in the 4CA group, which is nearly double. These results are consistent with published data [1,8,18]. There were no postsurgical complications after PRC. In the 4CA group, two patients had signs of nonunion at the review and one had a broken screw. When the patients initially excluded because of complete wrist fusion after PRC (4 patients) or 4CA (1 patient) are included in the analysis, the complication rate was 33% (4/12) for the 4CA group versus 15% (4/26) for the PRC group. This suggests that a selection bias is present: the four PRC cases and one 4CA case that were excluded reduced the number of failures. Another bias was the difference in the length of follow-up at review: 50 months for the PRC group versus 27 months for the 4CA group. However, since the outcomes of these types of procedures are considered stable after 2 years, these groups were comparable. In terms of indications for surgery, other than Kienböck’s disease being an indication only for PRC, they were the same for both groups: 2/ 3 SNAC wrist and 1/3 SLAC wrist. The second part of the study sought to explore the link between CH, tendon excursion and grip strength using cadavers. While the results were as expected, our anatomical and radiographic study provided us with information that can be used to infer the consequences of each procedure on tendon
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P. Laronde et al. / Hand Surgery and Rehabilitation 35 (2016) 100–106 Table 1 Normal tendon excursion (Boyes [29]) and consequences on wrist and finger movements of reducing carpal height by 1 cm for proximal row carpectomy (PRC), 1 mm for four-corner arthrodesis (4CA). Muscle
Normal excursion Boyes [26]
Reduction in excursion after PRC (%)
Reduction in excursion after 4CA (%)
ECRB ECRL ECU FCU FCR
3.6 cm 3.7 cm 3.3 cm 3.3 cm 4.0 cm
27.8 27 30 30 25
2.8 2.7 3.0 3.0 2.5
ECRB: extensor carpi radialis brevis; ECRL: extensor carpi radialis longus; ECU: extensor carpi ulnaris; FCU: flexor carpi ulnaris; FCR: flexor carpi radialis.
Fig. 4. Kienböck’s disease before (a) and after (b) proximal row carpectomy.
excursion and postoperative strength. We were able to obtain statistically significant results because the two groups in the anatomical study were initially similar. In the 4CA technique first described by Watson et al. [26], fixation of the arthrodesis, followed by decortication and filling of the resulting defects with bone graft were intended to maintain the CH. We decided to perform minimal decortication of the bone surfaces so that bone grafting would not be necessary, thereby keeping the CH as close as possible to that obtained using Watson’s technique. The resulting loss in CH was negligible (3%). The postoperative CH was statistically different between the two groups, and corresponded generally to the lunate’s height [16,27]. This outcome is the maximum height a surgeon can expect after 4CA in minimally deformed wrists, with little decortication and complete reduction of the lunate and triquetrum on the capitate and hamate. But in reality, the CH is often slightly less, as we found in our clinical study: 0.50 vs 0.52. In cases of severe joint destruction, the preoperative CH is often already reduced. This was the case for two pathological wrists in our study (stage IIIB Kienböck disease according to Lichtman’s classification [28] and lunotriquetral instability): the difference in preoperative CH between the left and right wrists was greater than 3 mm, while the difference in the postoperative CH was less than the mean value (Fig. 4). The excess space between the capitate and lunate fossa of the radius, observed after PRC (Fig. 3), fully illustrates the principle of loss of tendon excursion. Tendon excursion can be defined as a length reserve for tendon motion during flexion and extension movements. Boyes [29] measured tendon excursion for wrist and finger tendons (Table 1). The theoretical consequence of CH reduction on tendon excursion and strength can be calculated for the PRC and 4CA procedures. PRC reduces tendon excursion of the wrist motor muscles by 25– 30%, versus only 2.5–3% for 4CA (Table 1), which is 10 times less. This reduction in tendon excursion is proportional to the reduction in CH (Table 1). According to the length–tension
diagram for a muscle-tendon unit [30,31], maximum muscle power is developed in the middle two-thirds of the tendon’s excursion. Reducing tendon excursion by 25–30% should inevitably reduce the resulting muscle power to a greater degree for PRC than 4CA. This has already been shown for pathologies affecting the radius, scaphoid [32–34], metacarpals [35] and humerus [36]. For example, the extension strength of the triceps is reduced 17% for 1 cm of humerus shortening, 40% for 2 cm and 63% for 3 cm [36]. What are the practical clinical consequences for PRC? The loss of CH results in an imbalance between skeleton length and tendon length. A portion of the tension developed by the muscle-tendon units in the wrist is used to hold the newly formed radiocapitate joint together. As a consequence, this muscle tension is no longer available to move the fingers; additional muscle activation is needed to restore full flexion and extension movements. Since these muscles are recruited beyond the optimal middle two-thirds of the tension-length curve and they cannot contract beyond a threshold, the result is a loss of strength [32–35,37]. Since the 4CA procedure preserves the CH, the length of the tendons that cross the wrist is unchanged, thereby reducing the possibility of muscle weakness [38]. Despite this, there is no published data showing strength to be superior with 4CA than with PRC [5,9,12,17,20], as we found in this clinical study. There are several possible explanations: first, the muscles adapt to the decreased distance between the proximal and distal attachments of the muscle-tendon unit following PRC. The muscle body gradually remodels itself to return to its optimal length on the length–tension curve, which allows the strength to recover in the PRC group [39]; however, this is no experimental proof of this. Another factor may be the increased joint stresses due to changes in the joint spaces. In a normal wrist, the movements mainly occur at the radiocarpal and mid-carpal joints. When the mid-carpal joint is fused after the 4CA procedure but the CH is maintained, the tension in the muscletendon units can increase. This is due to an increased moment arm on the carpus, which no longer bends at the mid-carpal joint. Conversely, PRC reduces CH and places noncongruent joints surfaces in contact, thereby reducing the joint stresses. This has been confirmed by DeBottis et al. who showed that
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more strength was needed to carry out the same movements after 4CA than in normal wrists. When compared to normal wrists, PRC requires less strength for the same movements [38]. These results were significant and demonstrated for the extensor carpi ulnaris, extensor carpi radialis brevis and longus, along with the flexor carpi ulnaris. The expected loss of strength after PRC due to reduced tendon excursion seems to be partially compensated by the reduction in strength needed to carry out movements [38]. This could explain the absence of significant differences in strength between PRC and 4CA procedures in most studies, including ours. It appears that the CH is not a major predictor for postoperative strength after PRC or 4CA. The debate between PRC and 4CA continues [1,8,10,11]. Advocates of 4CA believe that preserving the CH ensures the best possible postoperative strength, despite longer postoperative recovery and more postoperative complications (infection, nonunion, broken hardware) [3,5,9,12,17]. Proponents of PRC emphasize the relative simplicity of the procedure and the lower complication rate. Our study found PRC to be superior to 4CA in terms of postoperative strength, range of motion and clinical scores. It also calls into question the relationship between CH and postoperative strength. For common indications such as stage I and II SNAC and SLAC wrists, we advocate performing PRC based on the results of published studies and our own clinical study. If PRC is contraindicated, such as in cases of stage III SNAC and SLAC wrists, 4CA is still the best solution [1,2]. 5. Conclusion Neither our study nor other published studies provide evidence that 4CA is better than PRC. On the contrary, PRC leads to better outcomes relative to strength, joint range of motion and clinical scores. Our findings suggest that postoperative strength is not a function of residual carpal height alone. This can be explained by muscle and joint biomechanics: the reduction in tendon excursion after PRC is counterbalanced by the greater joint stresses after 4CA. Disclosure of interest Christian Fontaine: clinical trials: as co-investigator, secondary experimenter, collaborator in the study for Hospital and Healthcare Consulting. Conferences: invitations as contributor for Allergan, Baxter, IPSEN and MERZ. He has no other competing interest to disclose. Christophe Chantelot: clinical trials: acting as principal investigator, coordinator or main experimenter for Howmedica (Guepar) and Aston Medical Evolutive. Pascale Laronde, Nicolas Christiaens and Aurélien Aumar declare that they have no competing interest. Acknowledgements Thank you to Dr. Emmanuel Camus for his insights, Drs. Varenka Baratinski and Arthur Lasnier for their work on
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