NSW workers compensation guidelines for the evaluation of permanent impairment

3.8 When true leg length discrepancy is determined clinically (see AMA5 Section 17.2b, p 528), the method used must be indicated (eg tape measure from anterior superior iliac spine to the medial malleolus). Clinical assessment of leg length discrepancy is an acceptable method, but if full-length computerised tomography films are available, they should be used in preference. Such an examination should not be ordered solely for determining leg lengths.

3.9 Note that the figures for lower limb impairment in AMA5 table 17-4 (p 528) are incorrect. The correct figures are shown below.

AMA5 Table 17-4: Impairment due to limb length discrepancy

3.10 Assessment of gait derangement is only to be used as a method of last resort. Methods of impairment assessment most fitting the nature of the disorder should always be used in preference. If gait derangement (AMA5 Section 17.2c, p 529) is used, it cannot be combined with any other evaluation in the lower extremity section of AMA5.

3.11 Any walking aid used by the subject must be a permanent requirement and not temporary.

3.12 In the application of AMA5 Table 17-5 (p 529), delete item ‘b’, as the Trendelenburg sign is not sufficiently reliable.

3.13 AMA5 Section 17.2d (p 530) is not applicable if the limb other than that being assessed is abnormal (eg if varicose veins cause swelling, or if there is another injury or condition which has contributed to the disparity in size).

3.14 Note that the figures for lower limb impairment given in AMA5 Table 17-6 (p 530) are incorrect. The correct figures are shown below.

AMA5 Table 17-6: Impairment due to unilateral leg muscle atrophy

3.15 The Medical Research Council gradings for muscle strength are universally accepted. They are not linear in their application, but ordinal. Only the six grades (0–5) should be used, as they are reproducible among experienced assessors. The descriptions in AMA5 Table 17-7 (p 531) are correct. The results of electrodiagnostic methods and tests are not to be considered in evaluating muscle testing, which can be performed manually. AMA5 Table 17-8 (p 532) is to be used for this method of evaluation.

3.16 Although range of motion (ROM) appears to be a suitable method for evaluating impairment (see AMA5 Section 17.2f, pp 533–38), it may be subject to variation because of pain during motion at different times of examination, possible lack of cooperation by the person being assessed and inconsistency. If there is such inconsistency, then ROM cannot be used as a valid parameter of impairment evaluation.

AMA5 Table 17-10 (p 537) is misleading as it has valgus and varus deformity in the same table as restriction of movement, possibly suggesting that these impairments may be combined. This is not the case. Any valgus/ varus deformity present which is due to the underlying lateral or medial compartment arthritis, cannot be combined with loss of range of movement. Therefore, when faced with an assessment in which there is a rateable loss of range of movement as well as a rateable deformity, calculate both impairments and use the greater. Valgus and varus knee angulation are to be measured in a weight-bearing position using a goniometer. It is important to bear in mind that valgus and/or varus alignments of the knee may be constitutional. It is also important to always compare with the opposite knee.

3.17 If range of motion is used as an assessment measure, then AMA5 Tables 17-9 to 17 14 (p 537) are selected for the joint or joints being tested. If a joint has more than one plane of motion, the impairment assessments for the different planes should be added. For example, any impairment of the six principal directions of motion of the hip joint are added (see AMA5, p 533).

In AMA5 Table 17-10 (p 537), on knee impairment, the sentence should read: ‘Deformity measured by femoral-tibial angle; 3° to 9° valgus is considered normal’.

In AMA5 Table 17-11 (ankle motion) the range for mild flexion contracture should be one to 10°, for moderate flexion contracture it should be 11° to 19°, and for severe flexion contracture it should be 20° plus.

The revised Table 17-11 is below.

AMA5 Table 17-11: Ankle motion impairment estimates

When calculating impairment for loss of range of movement, it is most important to always compare measurements of the relevant joint(s) in both extremities. If a contralateral ‘normal/uninjured’ joint has less than average mobility, the impairment value(s) corresponding to the uninvolved joint serves as a baseline, and is subtracted from the calculated impairment for the involved joint. The rationale for this decision should be explained in the assessor’s report (see AMA5 Section 16.4c, p 454).

3.18 Ankylosis is to be regarded as the equivalent to arthrodesis in impairment terms only. For the assessment of impairment, when a joint is ankylosed (AMA5 section 17.2g, pp 538-543), the calculation to be applied is to select the impairment if the joint is ankylosed in optimum position (see table 3.1 below), and then if not ankylosed in the optimum position, by adding (not combining) the values of percentage of WPI using tables 17-15 to 17-30 (pp 538-543 AMA5).

Table 3.1: Impairment for ankylosis in the optimum position

Note that the figures in Table 3.1 suggested for ankle impairment are greater than those suggested in AMA5.

Ankylosis of the ankle in the neutral/optimal position equates with 15 (37) [53]% impairment as per Table 3.1. Table 3.1(a) is provided below as a guide to evaluate additional impairment owing to variation from the neutral position. The additional amounts at the top of each column are added to the figure for impairment in the neutral position. In keeping with the value given on page 541 of AMA5, the maximum impairment for ankylosis of the ankle remains at 25 (62) [88]% impairment.

Table 3.1(a): Impairment for ankylosis in variation from the optimum position

3.19 Impairment due to arthritis (AMA5 Section 17.2n, pp 544–45) following a work-related injury is uncommon, but may occur in isolated cases. The presence of arthritis may indicate a pre-existing condition and this should be assessed and an appropriate deduction made (see Chapter 1).

3.20 The presence of osteoarthritis is defined as cartilage loss. Cartilage loss can be measured by properly aligned plain X-ray, or by direct vision (arthroscopy), but impairment can only be assessed according to the radiologically determined cartilage loss intervals shown in AMA5 Table 17-31 (p 544). When assessing impairment of the knee joint, which has three compartments, only the compartment with the major impairment is used in the assessment. That is, measured impairments in the different compartments cannot be added or combined.

3.21 Detecting the subtle changes of cartilage loss on plain radiography requires comparison with the normal side. All joints should be imaged directly through the joint space, with no overlapping of bones. If comparison views are not available, AMA5 Table 17-31 (p 544) is used as a guide to assess joint space narrowing.

3.22 One should be cautious in making a diagnosis of cartilage loss on plain radiography if secondary features of osteoarthritis, such as osteophytes, subarticular cysts or subchondral sclerosis are lacking, unless the other side is available for comparison. The presence of an intra-articular fracture with a step in the articular margin in the weight-bearing area implies cartilage loss.

3.23 The accurate radiographic assessment of joints always requires at least two views. In some cases, further supplementary views will optimise the detection of joint space narrowing or the secondary signs of osteoarthritis.

Sacro-iliac joint: Being a complex joint, modest alterations are not detected on radiographs, and cross sectional imaging may be required. Radiographic manifestations accompany pathological alterations. The joint space measures between 2mm and 5mm. Osteophyte formation is a prominent characteristic of osteoarthritis of the sacro-iliac joint.

Hip: An anteroposterior view of the pelvis and a lateral view of the affected hip are ideal. If the affected hip joint space is narrower than the asymptomatic side, cartilage loss is regarded as being present. If the anteroposterior view of the pelvis has been obtained with the patient supine, it is important to compare the medial joint space of each hip, as well as superior joint space, as this may be the only site of apparent change. If both sides are symmetrical, then other features, such as osteophytes, subarticular cyst formation, and calcar thickening, should be taken into account to make a diagnosis of osteoarthritis.

Knee – Tibio-femoral joint: The best view for assessment of cartilage loss in the knee is usually the erect intercondylar projection, as this profiles and stresses the major weight-bearing area of the joint, which lies posterior to the centre of the long axis. The ideal X-ray is a posteroanterior view, with the patient standing, knees slightly flexed, and the X-ray beam angled parallel to the tibial plateau (Rosenberg view). Both knees can be readily assessed with the one exposure. It should be recognised that joint space narrowing in the knee does not necessarily equate with articular cartilage loss, as deficiency or displacement of the menisci can also have this effect. Secondary features, such as subchondral bone change and past surgical history, must also be taken into account.

Knee – Patello-femoral joint: This should be assessed in the ‘skyline’ view, again preferably with the other side for comparison. The X-ray should be taken with 30 degrees of knee flexion to ensure that the patella is load-bearing and has engaged the articular surface femoral groove.

• Footnote to AMA5 Table 17-31 (p 544) regarding patello-femoral pain and crepitation:
  • This item is only to be used if there is a history of direct injury to the front of the knee, or in cases of patellar translocation/dislocation without direct anterior trauma. This item cannot be used as an additional impairment when assessing arthritis of the knee joint itself, of which it forms a component. If patello-femoral crepitus occurs in isolation (ie with no other signs of arthritis) following either of the above, then it can be combined with other diagnosis-based estimates (AMA5 Table 17-33, p 546). Signs of crepitus need to be present at least one year post-injury.
• Note: Osteoarthritis of the patello-femoral joint cannot be used as an additional impairment when assessing arthritis of the knee joint itself, of which it forms a component.

Ankle: The ankle should be assessed in the mortice view (preferably weight-bearing), with comparison views of the other side, although this is not as necessary as with the hip and knee.

Subtalar: This joint is better assessed by CT (in the coronal plane) than by plain radiography. The complex nature of the joint does not lend itself to accurate and easy plain X-ray assessment of osteoarthritis.

Talonavicular and calcaneocuboid: Anteroposterior and lateral views are necessary. Osteophytes may assist in making the diagnosis.

Intercuneiform and other intertarsal joints: Joint space narrowing may be difficult to assess on plain radiography. CT (in the axial plane) may be required. Associated osteophytes and subarticular cysts are useful adjuncts to making the diagnosis of osteoarthritis in these small joints.

Great toe metatarsophalangeal: Anteroposterior and lateral views are required. Comparison with the other side may be necessary. Secondary signs may be useful.

Interphalangeal: It is difficult to assess small joints without taking secondary signs into account. The plantar-dorsal view may be required to get through the joints, in a foot with flexed toes.

3.24 If arthritis is used as the basis for assessing impairment, then the rating cannot be combined with gait disturbance, muscle atrophy, muscle strength or range of movement assessments. It can be combined with a diagnosis-based estimate (AMA5 Table 17-2, p 526).

3.25 Where there has been amputation of part of a lower extremity Table 17-32 (p 545, AMA5) applies. In that table, the references to three inches for below the knee amputation should be converted to 7.5cm.

3.26 AMA5 Section 17.2j (pp 545–49) lists a number of conditions that fit a category of diagnosis-based estimates. They are listed in AMA5 Tables 17-33, 17-34 and 17-35 (pp 546–49). When using this table it is essential to read the footnotes carefully. The category of mild cruciate and collateral ligament laxity has inadvertently been omitted in Table 17-33. The appropriate rating is 5 (12)% whole person (lower extremity) impairment.

3.27 It is possible to combine impairments from Tables 17-33, 17-34 and 17-35 for diagnosis-related estimates with other components (eg nerve injury) using the Combined Values Chart (AMA5, pp 604–06) after first referring to the Guidelines for the appropriate combination of evaluation methods (see Table 3.5).

3.28  Pelvic fractures: Pelvic fractures are to be assessed as per Table 4.3 in Chapter 4 the Guidelines, and not as per AMA5 Table 17-33 (p 546).

Hip: The item in relation to femoral neck fracture ‘malunion’ is not to be used in assessing impairment. Use other available methods.

Femoral osteotomy:

• Good result: 10 (25)
• Poor result: Estimate according to examination and arthritic degeneration

Tibial plateau fractures: Table 3.2 of the Guidelines (below), replaces the instructions for tibial plateau fractures in AMA5 Table 17-33 (p 546).

Table 3.2: Impairment for tibial plateau fractures

In deciding whether the fracture falls into the mild, moderate or severe categories, the assessor must take into account:

• the extent of involvement of the weight-bearing area of the tibial plateau
• the amount of displacement of the fracture(s)
• the amount of comminution present.

Patello-femoral joint replacement: Assess the knee impairment in the usual way and combine with 9% WPI (22% LEI) for isolated patello-femoral joint replacement.

Total ankle replacement:

Table 3.3: Rating for ankle replacement results

The points system for rating total ankle replacements is to be the same as for total hip and total knee replacements, with the following impairment ratings:

Tibia-os calcis angle: The table given below for the impairment of loss of the tibia-os calcis angle is to replace AMA5 Table 17-29 (p 542) and the section in AMA5 Table 17-3 (p 546) dealing with loss of tibia-os calcis angle. These two sections are contradictory, and neither gives a full range of loss of angle.

Table 3.4 Impairment for loss of the tibia-os calcis angle

Hindfoot intra-articular fractures: In the interpretation of AMA5 Table 17-33 (p 547, AMA5), reference to the hindfoot, intra-articular fractures, the words subtalar bone, talonavicular bone, and calcaneocuboid bone imply that the bone is displaced on one or both sides of the joint mentioned. To avoid the risk of double assessment, if avascular necrosis with collapse is used as the basis of impairment assessment, it cannot be combined with the relevant intra-articular fracture in Table 17-33, column 2. In Table 17-33, column 2, metatarsal fracture with loss of weight transfer means dorsal displacement of the metatarsal head.

Plantar fasciitis: If there are persistent symptoms and clinical findings after 18 months, this is rated as 2% LEI (1% WPI).

Resurfacing procedures: No additional impairment is to be awarded for resurfacing procedures used in the treatment of localised cartilage lesions and defects in major joints.

3.29  AMA5 tables 17-34 and 17-35 (pp 548–49) use a different concept of evaluation. A point score system is applied, and then the total points calculated for the hip (or knee) joint are converted to an impairment rating from Table 17-33. Tables 17-34 and 17-35 refer to hip and knee joint replacements respectively. Note that, while all the points are added in Table 17-34, some points are deducted when Table 17-35 is used. (Note that hemiarthroplasty rates the same as total joint replacement.)

3.30 In respect of ‘distance walked’ under ‘b. Function’ in AMA5 Table 17-34 (p 548), the distance of six blocks should be construed as 600 metres, and three blocks as 300 metres.

Note that AMA5 Table 17-35 (p 549) is incorrect. The correct table is shown below:

AMA5 Table 17-35: Rating knee replacement results

* Refer to the unaffected limb to take into account any constitutional variation.

3.31 Skin loss (AMA5 p 550) can only be included in the calculation of impairment if it is in certain sites and meets the criteria listed in AMA5 Table 17-36 (p 550).

3.32 When assessing the impairment due to peripheral nerve injury (AMA5, pp 550–52) assessors should read the text in this section. Note that separate impairments for the motor, sensory and dysaesthetic components of nerve dysfunction in AMA5 Table 17-37 (p 552) are to be combined.

3.33 Note that the (posterior) tibial nerve is not included in Table 17-37, but its contribution can be calculated by subtracting ratings of common peroneal nerves from sciatic nerve ratings.

3.34 Peripheral nerve injury impairments can be combined with other impairments, but not those for gait derangement, muscle atrophy, muscle strength or complex regional pain syndrome, as shown in AMA5 Table 17-2 (p 526). Motor and sensory impairments given in Table 17-37 are for complete loss of function and assessors must still use Table 16-10 and 16-11 in association with Table 17-37.

3.35 Complex regional pain syndrome types 1 and 2 are to be assessed using the method in Chapter 17 of the Guidelines.

3.36 Lower extremity impairment due to vascular disorders (AMA5, pp 553–54) is evaluated using AMA5 Table 17-38 (p 554). Note that Table 17-38 gives values for lower extremity impairment, not WPI. In that table, there is a range of lower extremity impairments within each of the classes 1 to 5. As there is a clinical description of which conditions place a person’s lower extremity in a particular class, the assessor has a choice of impairment rating within a class, the value of which is left to the clinical judgement of the assessor.

3.37 When measuring dorsiflexion at the ankle, the test is carried out initially with the knee in extension and then repeated with the knee flexed to 45 degrees. The average of the maximum angles represents the dorsiflexion range of motion (AMA5 Figure 17-5, p 535).

Table 3.5: Lower extremity worksheet

Potential impairment is the impairment percentage for that method of assessment. Selected impairment is the impairment, or impairments selected, that can be legitimately combined with other lower extremity impairments to give a final lower extremity impairment rating.